I also had the same problem after an update on a AMD A6-6400 processor with a Radeon HD GPU. Got the black screen of death (BSOD). I was able to boot up (sometimes) holding down the shift key to display the GRUB menu, selecting "Advanced options for Ubuntu" and then selecting a previous version of the kernel (3.13.0-40-generic).
Update V - System rebuild
My AMD processor is mounted on a Gigabyte GA-F2A88XN-blah-blah-blah motherboard with retrofit quiet cooling components. I hate noise. I like this system when it works properly because I can't hear it. Don't suggest I change the hardware. That is not going to happen.
The Old System
I had Ubuntu 14.04 LTS (32 bit) installed with the proprietary fglrx drivers enabled. The open source drivers used too much CPU power. I could hear the fans. The open source drivers sucked.
This fglrx configuration worked fine for about a year. Then the 14.04 automatic updates stopped working. More BSOD bullshit. That kind of thing. Enough is enough.
The New System
The new system started with Ubuntu 15.10 (64 bit) installed with the open-source drivers enabled. Everything seemed to work. I then enabled the fglrx drivers. Everything seemed to work. WooHoo. Time for lunch.
For some reason, after some time had passed, the custom cooling fans began to run at maximum speed. My black box was noisy and annoying.
The sun was shining on the box and it was a warm day, but the CPU should have been napping. Now it sounded like it was competing in the Tour-de-France.
I powered up the TV, turned on the remote keyboard. Make sure the proper HDMI input is selected. This takes probably 45 seconds. The box, meanwhile, is screaming for air. The Black Screen Of Death (BSOD) is the only response. This procedure takes more than 45 seconds.
So I press & hold the front-panel power button. I count to 10. Slowly. Nothing happens. WTF?!? I wait a bit more because I don't know what to do. Never had this happen before.
So then I pull the power cord.
Recovery from this condition is a bit complicated, but it can be done. I would tell you how I did this but I forget now and Your Mileage May Vary (YMMV) anyway. Just ask Volkswagon.
Short version: AMD A6-6400 on a Gigabyte GA-F2A... motherboard? Install Ubuntu 15.10 64 bit. Use the open source drivers. That works best.
I have since altered a line in /etc/default/grub from
GRUB_DEFAULT="Advanced options for Ubuntu>Ubuntu, with Linux 3.13.0-40-generic"
Note the text in the quotation marks is the exact same text as it appears on the 2 levels of GRUB menus. Adjust according to what appears on your own display.
After saving the edit, run the command:
This is not a solution of course, just a workaround, but at least it does boot up normally and everything seems to work. I hope a future update will make this problem go away. This last update was a total nightmare!
The latest kernel update (188.8.131.52) crippled my system. I am now using the latest AMD proprietary drivers and everything works again. This was another painful update. So now I'm thinking of using something other than Ubuntu. Seriously.
As reported below, the latest Linux kernel update (3.13.0-44) corrected the problem for me because I apparently use the Radeon driver. The problem was reported Dec 14 but it took almost a full month to correct the problem.
But wait! There's more! Apparently Kernel 3.13.0-44 has problems with NVIDIA drivers.
This morning (Jan 13) the software updater downloaded Linux kernel 3.13.0-44. It works on the A6-6400 on reboot. The file /etc/default/grub is back to its original form.
For the record, I also attempted to use several variations of the AMD fglrx suite of packages. It worked with the both the -40 and -43 releases BUT the rendered display was the wrong size! It turned a 50" HD TV into a 46" HD-ready TV. The smaller display was centered within the 50" display area. Very strange.