It might be a defective HARD DRIVE or a few other things.
Two things to test:
1) confirm you can boot into BIOS
2) boot to MEMTEST disc if possible and test your memory ( www.memtest.org )
3) create an Ubuntu boot disc and run from DVD (don't install) to see if that works to test your hardware.
If it's your HARD DRIVE, you need to determine if the drive is completely dead, or whether it's just corrupted SOFTWARE on the drive.
There is RECOVERY SOFTWARE that can attempt to rebuild your boot files but I don't want to get too far ahead of the problem so I'll just leave it there.