I long ago came to the conclusion that PC's take at least ten minutes to sort themselves out. Seven years of working with them day in, day out, has done absolutely nothing to persuade me otherwise!
I'm glad other people have found the same. At work we found a load of computer bits in a skip, so my resident computer geek managed to build a server out of them. Linked it all up, did all the networky stuff, all IP addresses the same, all speaking the same language - nothing. Re-booted the whole thing, went out for a fag, comes back in and everything is working! Extended 'network testing session' then followed - a 5-way HalfLife game