Sounds like a hard disk failure. Could also be the power source, or some capacitors on the motherboard, or a memory issue. If you can, burn yourself the
Ultimate Boot CD and run some tests. I'd first recommend a hard disk test, since you seem not to have any important data on your disk, based on the fact you tried a reinstall. Run either one by the manufacturer or IBM or Seagate. If you pass it, run Memtest+ for some rounds. Check the motherboard for swollen capacitors. They should have a flat top. If all this seems ok, try with another power source. Good luck.