Here is my problem.
When I add "nomodeset" option to /etc/default/grub in GRUB_CMDLINE_LINUX_DEFAULT, my laptop fails to recognize external monitor. No external monitor under system display setting. And there are always multiple background compiz processes running with constant noises (from fan). When I remove "nomodeset" option, my ubuntu sometimes (not always) hangs on booting (on the loading page).
It seems that this might result from nouveau driver, but I'm not sure. Can anyone tell me how to fix this? Any help would be appreciated!