I have been running Ubuntu on my computer for a long time, and I have been using 11.10 since it became available in October.

Suddenly, this morning, when I rebooted, the computer would not reach the log in screen. I go through the standard POST boot sequence, and I also get a splash screen for my Nvidia graphics card, so at least most of the hardware seems to be working.

After that, all I get is a flashing text prompt - one blinking white underline character on a screen that is otherwise completely blank. I don't think it is even reaching GRUB.

No key input is possible. I have tried various key combinations to try and initiate some kind of interface, be it command line or anything else. The only key combination that works is [CTRL]+[ALT]+[Delete] to reboot.

I realize this is likely to be a hardware problem, but it could be an Ubuntu problem(?), so I'm hoping for a specific set of troubleshooting steps so I can diagnose and repair this issue.

My current suspicion is that one of the drives in my 2 disk software RAID has failed (even though they should be too new for that). However, this computer is critical to my work, so I'd like to invite advice on any possibilities so as to waste as little time as possible in fixing this machine.