I've had the same problem on my 3000+ winchester when I had it overclocked. Around 2.1Ghz it would say "System boot fail due to CPU overclocking". Everytime I heard that damn voice I wanted to destroy something. Since then though, my bios failed (****!!!!) and I had to go back to the original one and didn't bother overclocking again, since I didn't see any improvement anyways.
maybe i'll try oc'ing again, but for now I gotta figure out whats wrong with this piece of **** video card, because I'm getting artifacts and its not even OC'ed. And HL2 runs like complete **** at higher than medium settings, with full detail.