you could have a fialing hard drive...hit esc or tab during the bootup HP screen to see if there are any SMART errors or something...also run a chkdisk to see if there is anything like bad sectors. Oh, and the BIOS might have some sort of diagnostic, and if not check the HP message boards, there usually are some built in diagnostics you can run with a few keystrokes to check for bad hardware.

1999 Silver Frost SVT #609 of 2760 Quaife, lightened SVT Flywheel, SPEC stage II clutch, removed resonator, k&n drop in - various other goodies too.