Another option to remember (just happened to me last night)...
Machine starts to boot, get past grub menu and then just a blank screen...tried re-booting with USB key, same behaviour...
Unplugged everything (powere, all USB cables, etc. -- there was an iPod Nano and an iPod Touch charging on the PC), plugged AC, keyboard and mouse and try again...BINGO, boots up. Plug remaining devices (including USB WI-FI), log in and everything working...
Just an FYI for other readers.
