I installed the NIC card when the device mgr. did not recognize the network adapter. When I did, the system would shut down immediately.

We are getting ready for severe storms, so I will be logging off and using that time to strip down the system as you suggested. Will keep you updated once the storms have passed........Okay.

Examine the built-in ethernet PORT; loose, shorted, pins bent, etc. Replace the NIC card with a new one. Sounds like you got a bad one.I've had the same problem. I replaced every component in the system, even the case. Still shuts down shortly after boot up. I initially suspected the motherboard, but my brand new one had the same issues. I've got new RAM, Vid card, HD, ect.. everything except the sound card. I could build a new system, if I could keep "them" running long enough. Oh yeah, I also put a new processor in the system...still the same shutdown shortly after boot up. I'm still CLUELESS. Going back to the basic system and reminding myself not to throw computer parts at the wall when i get mad OK, many deep breaths later... I realized my processor heatsink wasn't properly seated. Hard to believe, but these things are running so hot (not overclocked) that one improperly set heatsink pin was enough to allow the processor to overheat Well, its all good now, the system runs like a champ, and I've got enough new parts to make myself a new system. My wife thinks its a CONSPIRACY, but I swear I was just TRYING to fix the comp , I also added new thermal compound to the processor and CLEANED all the boards and fans. Good luck all!Congrats! But, I'm curious - you cleaned the CPU and re-applied thermal paste AFTER you had a problem, then, more new parts later, determined that it was a bad CPU install; hmmm, I'm not so sure that your wife isn't right!

Best of luck!