This is the second time this problem happened to me and I seriously don't want to do a fresh Ubuntu reinstall again. I was messing around with desktop environments and installed Xubuntu, KDE, and I didn't like the login screen so I reverted back to the Unity one. My games worked fine on Xubuntu and Unity, but the problems happened after I tried to install Plasma, where the first install attempt failed so I had to reset some settings in order to have a succesful second attempt.
The same kind of problem happened to me when I first tried to install Steam on Unity (which I managed to fix by doing a fresh Ubuntu reinstall):
At first, Steam wouldn't launch, but I've found the solution with some quick googling. Then, the games wouldn't launch. (nothing happens after the "preparing to launch game" window closes) The game's process is running though (with ~10mb memory).
I have the correct Mesa drivers installed for my AMD GPU and my OpenGL is up to date.
Here's the log when I try to open a game like Counter-Strike: Global Offensive:
Game update: AppID 730 "Counter-Strike: Global Offensive", ProcID 9488, IP 0.0.0.0:0 ERROR: ld.so: object '/home/ld/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored. ERROR: ld.so: object '/home/ld/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored. /bin/bash: /home/ld/.local/share/Steam/ubuntu12_32/steam-runtime/amd64/lib/x86_64-linux-gnu/libtinfo.so.5: no version information available (required by /bin/bash) pid 9491 != 9490, skipping destruction (fork without exec?) ERROR: ld.so: object '/home/ld/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored. ERROR: ld.so: object '/home/ld/.local/share/Steam/ubuntu12_32/gameoverlayrenderer.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS32): ignored. libGL error: unable to load driver: r600_dri.so libGL error: driver pointer missing libGL error: failed to load driver: r600 libGL error: unable to load driver: swrast_dri.so libGL error: failed to load driver: swrast CListHash::BLoadFromDisk: Could not load file /home/ld/.local/share/Steam/ubuntu12_32/config/filterlist.vdf into buffer. Generating new string page texture 389: 16x256, total string texture memory is 2.03 MB
Here's the log when I'm trying to open Steam:
Running Steam on ubuntu 16.04 64-bit
STEAM_RUNTIME is enabled automatically
grep: symbol lookup error: grep: undefined symbol: pcre_jit_stack_alloc
grep: symbol lookup error: grep: undefined symbol: pcre_jit_stack_alloc
grep: symbol lookup error: grep: undefined symbol: pcre_jit_stack_alloc
/bin/bash: /home/ld/.local/share/Steam/ubuntu12_32/steam-runtime/amd64/lib/x86_64-linux-gnu/libtinfo.so.5: no version information available (required by /bin/bash)
awk: /home/ld/.local/share/Steam/ubuntu12_32/steam-runtime/amd64/lib/x86_64-linux-gnu/libtinfo.so.5: no version information available (required by /lib/x86_64-linux-gnu/libreadline.so.6)
Installing breakpad exception handler for appid(steam)/version(1471977975)
Installing breakpad exception handler for appid(steam)/version(1471977975)
Gtk-Message: Failed to load module "gail"
Gtk-Message: Failed to load module "atk-bridge"
Gtk-Message: Failed to load module "unity-gtk-module"
Installing breakpad exception handler for appid(steam)/version(1471977975)
Fontconfig error: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 72: non-double matrix element
Fontconfig error: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 72: non-double matrix element
Fontconfig warning: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 80: saw unknown, expected number
[0920/091737:ERROR:main_delegate.cc(779)] Could not load cef_extensions.pak
[0920/091737:ERROR:browser_main_loop.cc(217)] Running without the SUID sandbox! See https://chromium.googlesource.com/chromium/src/+/master/docs/linux_suid_sandbox_development.md for more information on developing with the sandbox on.
Installing breakpad exception handler for appid(steamwebhelper)/version(20160823182455)
Installing breakpad exception handler for appid(steamwebhelper)/version(1471976695)
[0920/091737:ERROR:main_delegate.cc(779)] Could not load cef_extensions.pak
Installing breakpad exception handler for appid(steamwebhelper)/version(20160823182455)
Installing breakpad exception handler for appid(steamwebhelper)/version(1471977975)
Installing breakpad exception handler for appid(steamwebhelper)/version(1471977975)
Installing breakpad exception handler for appid(steam)/version(1471977975)
Installing breakpad exception handler for appid(steam)/version(1471977975)
Installing breakpad exception handler for appid(steam)/version(1471977975)
Installing breakpad exception handler for appid(steam)/version(1471977975)
Installing breakpad exception handler for appid(steam)/version(1471977975)
Installing breakpad exception handler for appid(steam)/version(1471977975)
Created shared memory when not owner SteamController_Shared_mem
Installing breakpad exception handler for appid(steam)/version(1471977975)
Installing breakpad exception handler for appid(steam)/version(1471977975)</pre>
** (steam:9298): WARNING **: Unknown device type 14
** (steam:9298): WARNING **: Could not create object for /org/freedesktop/NetworkManager/Devices/2: unknown object type
Installing breakpad exception handler for appid(steam)/version(1471977975)
** (steam:9298): WARNING **: Ignoring invalid property 'secondaries'
** (steam:9298): WARNING **: Ignoring invalid property 'autoconnect-priority'
** (steam:9298): WARNING **: Ignoring invalid property 'route-data'
** (steam:9298): WARNING **: Ignoring invalid property 'address-data'
** (steam:9298): WARNING **: Ignoring invalid property 'route-data'
** (steam:9298): WARNING **: Ignoring invalid property 'address-data'
** (steam:9298): WARNING **: Ignoring invalid property 'secondaries'
** (steam:9298): WARNING **: Ignoring invalid property 'autoconnect-priority'
** (steam:9298): WARNING **: Ignoring invalid property 'route-data'
** (steam:9298): WARNING **: Ignoring invalid property 'address-data'
** (steam:9298): WARNING **: Ignoring invalid property 'route-data'
** (steam:9298): WARNING **: Ignoring invalid property 'address-data'
Generating new string page texture 2: 48x256, total string texture memory is 49.15 KB Generating new string page texture 3: 256x256, total string texture memory is 311.30 KB Installing breakpad exception handler for appid(steam)/version(1471977975) Installing breakpad exception handler for appid(steam)/version(1471977975) Installing breakpad exception handler for appid(steam)/version(1471977975) roaming config store loaded successfully - 340 bytes. migrating temporary roaming config store Fontconfig error: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 72: non-double matrix element Fontconfig error: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 72: non-double matrix element Fontconfig warning: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 80: saw unknown, expected number Installing breakpad exception handler for appid(steam)/version(1471977975) Failed to init SteamVR because it isn't installed ExecCommandLine: ""/home/ld/.local/share/Steam/ubuntu12_32/steam" " Installing breakpad exception handler for appid(steam)/version(1471977975) System startup time: 3.66 seconds bash: /home/ld/.local/share/Steam/ubuntu12_32/steam-runtime/amd64/lib/x86_64-linux-gnu/libtinfo.so.5: no version information available (required by bash) grep: symbol lookup error: grep: undefined symbol: pcre_jit_stack_alloc grep: symbol lookup error: grep: undefined symbol: pcre_jit_stack_alloc Generating new string page texture 73: 128x256, total string texture memory is 442.37 KB Generating new string page texture 74: 128x256, total string texture memory is 131.07 KB Generating new string page texture 75: 64x256, total string texture memory is 507.90 KB Generating new string page texture 76: 8x256, total string texture memory is 516.10 KB Generating new string page texture 77: 32x256, total string texture memory is 548.86 KB Running Steam on ubuntu 16.04 64-bit STEAM_RUNTIME has been set by the user to: /home/ld/.local/share/Steam/ubuntu12_32/steam-runtime /bin/bash: /home/ld/.local/share/Steam/ubuntu12_32/steam-runtime/amd64/lib/x86_64-linux-gnu/libtinfo.so.5: no version information available (required by /bin/bash) grep: symbol lookup error: grep: undefined symbol: pcre_jit_stack_alloc grep: symbol lookup error: grep: undefined symbol: pcre_jit_stack_alloc grep: symbol lookup error: grep: undefined symbol: pcre_jit_stack_alloc awk: /home/ld/.local/share/Steam/ubuntu12_32/steam-runtime/amd64/lib/x86_64-linux-gnu/libtinfo.so.5: no version information available (required by /lib/x86_64-linux-gnu/libreadline.so.6) /usr/bin/ldd: line 119: printf: write error: Broken pipe ExecCommandLine: "/home/ld/.local/share/Steam/ubuntu12_32/steam steam://open/driverhelperready" ExecSteamURL: "steam://open/driverhelperready" Generating new string page texture 126: 256x256, total string texture memory is 811.01 KB Generating new string page texture 127: 128x256, total string texture memory is 942.08 KB Generating new string page texture 128: 384x256, total string texture memory is 1.34 MB Generating new string page texture 129: 24x256, total string texture memory is 1.36 MB Generating new string page texture 131: 128x256, total string texture memory is 1.49 MB Generating new string page texture 176: 64x256, total string texture memory is 196.61 KB Generating new string page texture 224: 512x256, total string texture memory is 2.02 MB
steamfrom a terminal and post back the output so we can help you.