hi my 2nd computer i built in 04, i recently installed a new seagate hd. 120 gb.s ata 133 as last hd. failed. ok so new hd. installed in jan.07 now it shuts down after maybe 10-20 min.s online i know heat is the issue here. but maybe motherboard is bad? im runnin windows xp pro, sp2 computer consists of, amd athlon 2800+, new ultra 550 w psu (installed 6-06) mb=shuttle an35,ultra 512 mb. pc2700, chaintech 440 8x agp video card. im certain cpu fan is operational, 2 tower fans operational, psu fans operational. any help would be apreciated just where do i start?