Service Pack 3 stops computer from booting

Hi guys. My computer is working awesomely. It's my old setup that my father was supposed to buy that is buggered.

- He has 4 gigabytes of Kingston / Corsair (?) DDR RAM.
- A8N-SLI motherboard. I believe I upgraded the BIOS to 1.14, the latest as of a few months ago.
- AMD 3500+ processor.
- Power supply might be 600 watts. Not sure.

He claims that it worked perfectly before he installed SP3 and apparently he was doing some sort of install last night and shutdown the computer after it had installed. Now the computer won't even boot up into Win XP AND it won't let him go into the BIOS.

I suspect he made a big mistake by touching the computer at all when he did. I tried hitting DEL / F5 / F8 upon boot by the computer simply says "Now entering Setup..." and does nothing else.

Any ideas? Thanks in advance!

EDIT: It looks like my suggestion of re-installing the hardware was the right idea. He shook (yes, shook) the case a little bit and it seems that it was a loose connection of sorts. I can't recommend shaking your computer case to solve any future issues, though!

Hi,
I'm running a ASUS M2N32-SLI Deluxe with AMD 5000+ BE. Installed SP3 and the computer ran fine. But what really bothered me was when I updated my video driver and " found new hardware" in XP comes up. No problem right. I install the new drivers and reboot. After the computer is on a message pops up saying I have three days to reactivate Windows because of a hardware change. I didn't change anything. I uninstalled SP3. Microsoft went too far this time. Try this out and see if it happens to anyone else.