At this point, I would put in another hard disk and reinstall Ubuntu. Maybe should have done this before because then you can see what is supposed to be there. If you have data in the database, then you can try to recover it. If not, you have a new system to work with.
Realize that it doesn't take much to run Linux compared to Windows. My 'fast' Ubuntu 8.04 system is a 1.5GHz P4 with 750MB of ram and 40GB hard, more than 50% free. It was running with only 512MB. I'm running it as a Desktop plus LAMP system.