Recently I added my old 8600GT as a physx card to my 250GTS on an Asus P5N-D. It worked fine for about a month and now suddenly it wont even POST or anything. Ive made no changes to anything since I put it in. I have a 600w dual 18A 12v rails psu, Q9450, 8GB ddr2 and everythings stock. The 8600GT works fine in 2 different computers, and an 8400gs and geforce 5750 both work in mine. I read something about that specific 8600gt not working in some Asus mb, but it makes no sense for it to suddenly stop working. Any ideas? I posted on the Nvidia forum and there aint even a single view... dunno if im even in the right section. Seems like a mobo problem. By the way, Im new here and am pretty knowledgable about computers. Been working/fixing them for about 10yrs.
It could be that the card is sensitive to power. Your 600watt PSU with Dual 18 amp +12 volt rails is not big according to today´s PSU standards. Incompatibility with a certain card in certain boards is something that I have not seen before.