A quick first step would be to reset the bios to default settings and then look through them to see if any are suspect, like the memory being incorrectly set in auto mode, trying to boot off wrong drive, etc.
Download and run MEMTEST
off a CD to see if it will pass.
edit: and what are you using for a boot drive, new drive or an old drive that had an OS already on it? will it boot from a system repair disk rather than the HDD?