[tlug] Computer won't boot after upgrade to Ubuntu 11.10

[Martin G <ebisumartin@example.com>]

I reported this on askubuntu.stackexchange.com, but I thought I'd
cross post here because this is a little critical for me.

There are some screenshots which may or may not be helpful here:
http://askubuntu.com/questions/65973/ubuntu-wont-boot-after-upgrade-to-11-10

Anyway, the short story is that after what seemed like a silky smooth
upgrade process, one of my computers won't boot up. (My other two
computers upgraded without a hitch, so at least it's not all bad.)

When I reboot, one of three things happens. It hangs at a blank purple
screen, it hangs at the screen with the Ubuntu logo and five orange
dots underneath, or, if I try to boot into recovery mode, it spits out
some cryptic text and hangs.

The text is:
No caching mode page present
Assuming drive cache write through
Attached SCSI disk

Other than that, I have no logs to work with because I can't get to
any prompt or SSH to the machine over the LAN.

[CTRL]+[F6] or [CTRL]+[BACKSPACE] while booting don't work. I tried
pressing [F6] immediately after GRUB finished, which I thought I read
on the net somewhere would help...

The usual suspects are the Nvidia graphics card, or maybe something to
do with my software RAID (2 500GB drives).

However, I have no idea what is actually happening, so I should be
open to any possibility.

Oh, and I removed any extraneous USB devices so as to hopefully avoid
any confusion.

Any ideas on what I can try to get my Ubuntu 11.10 to boot?

Or at least how I can poke at it so that it will tell me what's wrong?

Any advice would be much appreciated.

-- 
Dave M G