OK, quick background: I am a software developer and have built perhaps 30 systems in my life, and this is the first time I have every been this baffled. I have come here looking for help! Thank you in advance! Last week I woke up and walked over to my 6-month-old dev machine (it has worked flawlessly since Dec 07). It was hibernating. I moved the mouse, then tapped the space bar, but the system didn't respond. I hit the reset button and the system restarted. Here's where the problem is: The system comes on, stays up for 4-5 seconds, there are no beeps and it does not post, then it shuts down. It repeats this over and over until I shut the power supply off. Now then, before you give any advice, here is what I have done: I assumed it was the power supply, so I have replaced it twice. The current PSU is a Antec 850watt unit. I've tried multiple outlets and a different surge protector but the system still does the same thing! Then I assumed it was the Motherboard. I first tried a new ATX micro board from a local shop (the system still did the same thing) then I ordered a new MoBo from NewEgg. The system still does the same thing. I had the CPU checked out, and it was fine. Still, I bought a new one just to be safe and the system still does the same thing! I have replaced the video card with one that I know works (to prove it, I am using it now on this system to post this message). The video card swap did nothing- the system still did the same thing. I have not tried new RAM, but I took out all the RAM in hopes that it would post with a memory error, but the system still does the same thing. So, basically I am looking at a system with a new motherboard, a new CPU, a new power supply, all connections checked and re-checked a dozen times, with and without RAM, different video cards, hard drives connected but I've since disconnected those SATA cables as well, and still: The system comes on, stays up for 4-5 seconds, there are no beeps and it does not post, then it shuts down. It repeats this over and over until I shut the power supply off. Please, before I kill myself, can someone tell me what is wrong? My current specs (with all the new crap): Intel E8500 Core2 Duo CPU Gigabyte GA-EP35-DS4 motherboard Ballistix PC800 RAM (4 gig) MSI nVidia 8800GTX video card Antec 850watt PSU plus a few hard drives and a DVD drive that are not connected.