Ubuntu Natty doesn't boot anymore

Hey there,
it just began this morning that my beloved ThinkPad with Ubuntu Natty wouldn't boot anymore. Instead, I am always greeted by the terminal, now. [Well, actually 3 of 4 times the screen just stays purple, which must be due to this bug here (https://bugs.launchpad.net/ubuntu/+source/plymouth/+bug/771905). In this case I cannot even switch to the tty and usually have to reboot a few times till I get to the terminal at last.]

Anyways, I noticed that X is not running when I get to the terminal, so I tried to start X (does it make a difference whether I use X or the startx script?). X promptly showed the Nvidia logo as always and then a black screen. So I went to another tty and attempted to start Unity which was obviously not running – I didn't know whether to start it as root or as normal user, so I tried both – with the same result: a segmentation fault. Switching back to tty7, however, I could see and move the cursur, now (+ it was in the correct resolution). Also, "$ ps aux | grep unity" now delivered the unity processes (window-decorator, applications-daemon, files-daemon, panel-service). But other than that nothing had changed.

Taking a look at the log files (/var/log/syslog, /var/log/Xorg.0.log, /var/log/boot.log) I couldn't find any error messages or severe warnings, either. To me it looks like the boot process just stops before starting the graphical frontend.
Or rather hangs? Because it has happened like 3 or 4 times, now, that after some minutes of waiting and doing stuff in the console the graphical frontend suddenly would start as if nothing had happened. (Which is the only reason why I'm able to write to you, now.)

I really don't know what to do anymore. I already tried to generate a new X config via nvidia-xconfig, did a unity --reset and purged and reinstalled unity and ubuntu-desktop…
So, I'd be glad if you could help me especially since I'm having a giant pile of university work waiting for me. :( I'll happily give you logs and every other information you need. :)