Help - Unmountable Boot Volume

I have a 3Ghz Dell Dimension 4700, 512 mb ram, and an 80gb HD. It is about 9 months old.

I was trying to install an extension on Firefox and the computer froze up, so I had to reboot. When I did, I got this message when booting the computer. I cant boot in safe mode either. I did a search and found this but I still have a problem. When I boot the comp via my XP CD, I run chkdsk /r, but it stalls halfway through. It reaches 50% and it just hangs and never gets any further. I also looked on the Microsoft website and they said to also run fixboot if chkdsk doesnt work. I restarted the computer, ran fixboot instead, and tried to reboot but I get the same error message. Any and all help is appreciated.