Everyone is going the software/bios route, No harm there.
I work for HP, and i'm hardware side techy. Not saying i'm right, far from it, but here's a few suggestions that typically "can" help eliminate some possible causes.
Take out/disconnect most components. (Assuming you don't have raid, it shouldn't interfere).
If possible, do a cmos reset, or take out the battery on the board / boot without it, shut down, put it in, boot up, re "reset" the bios, and then go from there.
Clean cpu/heatsink. Use a can of compressed air, clean the socket, and the cpu pins (if any on either feature). Gently place it in, apply thermal paste/tape of choice.
Reseat the heatsink after its cleaned of course.
Re seat the dimms (memory). Reseat video, etc. Replug everything except the extra data harddrives.
At back of motherboard, only have mouse/keyboard plugged in + video cable. Sound is optional. (This eliminates any irq mismatches with 99% guarentee of clearing that issue up, ie usb hubs, etc).
Test boot in each idea if you think you're ready.
Then do a prime for 24hrs. Yes it's a power "waster", but well worth it. It's a proven app to bench,ark the f* outta ur pc, and make sure you're stable on stock.
Then try the unlock, overclock, etc. And re test prime again, for another 24hrs. Rinse repeat. Well worth it.
Hopefully this helps.
Alternatively... Try a spare blank hdd, install any windows, and prime 95 test from there. Might clear up any issues if the OS on your drive has to many errors.