Hmm you know I have this occasionally with my 2.4C on a P4P800-E Deluxe.
Sometimes, maybe once in 3 weeks, I will come home from work, turn on my PC and everything comes on, but no POST, nothing. THen I turn off, turn on again and its fine.

I always wondered why its so. I was thinking the mobo is slowly degrading from running at 250MHz FSB daily.