I've had this problem with random crashes with my new-ish computer which I haven't managed (or bothered) to pinpoint. It's something hardware related, but that's all I know. Last saturday the thing crashed once again and after I rebooted it, it wouldn't start. There was, on the console, some complaint about missing modules for INPUT products and a last line with nothing on but "pci", then nothing happened. I pressed enter a couple of times, decided it was broken and shut it down frustrated. Reiserfs3 has gotten some files confused when the system has crashed a few times (hooray for journaling... I should really try ext3/XFS/JFS/Reiser4), so I thought that it had finally screwed up something vital.
At the beginning of the week I downloaded a CD image of Knoppix, burnt it to a CD and and booted my computer with it. Worked like a charm (first time I used KDE in a while. Still not to my taste.) I wasn't feeling much like doing forensics on the piece of junk so I didn't properly get to it before today; fscking my HDs found nothing strange so I just reinstalled the kernel and rebooted the machine. The same problem. Then I started reading the boot process output a bit better; among other things I noticed it had already loaded pretty much everything including sound card and network adapter drivers and the error messages were about hotplug. Oh boy. The first thought was to again reboot with Knoppix and tinker with the boot process; the second one was to press Ctrl C.
Next time I'll try that first, not a week afterwards.