you could check that nothing else (like your RAM) came loose while you were changing out cards, or maybe you have to reset your CMOS settings (there should be a little jumper on your motherboard labeled "CMOS", "BIOS", "SETUP", something like that- just slide it over a peg, turn it on until it beeps and says it's reset, then put it back. make sure you're powered off before you move it though). But as Shadowex3 said, I'm surprised that little power supply could even get out enough to run the 8600.