When you say it freezes at the BIOS screen, does that mean it sometimes doesn't even boot as far as Win9x startup screen? If your computer is locking up at the BIOS screen from time to time, you may be looking at a hardware issue.

Check the usual things: Mobo manufacturer for possible BIOS updates; make sure your fans are all running, check for a possible heat issue. If all else fails, strip the system to bare minimum components (boot HD, video, mouse/keyboard), and start trouble-shooting from there.

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Somebody set up us the GPF!