Gaming PC, Elite Computer Group MB - NFORCE6M-A CPU - AMD Quad Core 9750 RAM - 8G DDR2 800 HD - 500GB Seagate GPU - GeForce 8600GT 512MB PSU - Logisys ATX 20/24 serial ATA 480W (3.3V, 5V, 12V, -5V, -12V) Symptoms and step to date. Rig shut down without warning, no power. Restart without successful post. Disconnected ATX12V, power stays on, but no post. Cleared BIOS, nothing. Stripped to the bones, MB, PSU, (1) 2GB RAM of (4) 2GB RAM (all identical) installed, cleared BIOS- successful post! Tested each RAM and slot, one at a time - all good. One RAM in any slot will post. Addition of any other RAM leads to no post, even with clearing BIOS, no matter what combination of RAM / slot is used. This is on an ESD mat with only the following right now: MB, PSU, GPU, HD, (1) 2GB RAM, CPU fan, USB mouse & keyboard, LCD monitor. I added everything else to make sure than my power supply wasn't failing. I thought it may be fluctuating, getting ready to fail, causing RAM voltage problems. So I added everything thinking that if it wouldn't post if that was the case, given the increase in power demand. Not the case, so I've ruled out the PSU. Processor must be good, since I'm using it to post this right now! No glitches, other than running slowly on only 2 GB RAM, rather than 8GB (I was only using 3.5GB anyways with 32 bit Vista Ultimate installed, I intend to upgrade.) Is there something I can do to check if the motherboard is going? I don't have another for bench testing. I don't think it's software, it's been running fine in this configuration for over a year, and always updated, cleaned, lots of ventilation with low operating temps and a high temp automatic shutoff that has never been needed. Plus a UPS. There was a squealing noise that happened on power up over a month ago. Made me worry because it happened two power-ups lasting for about 3 seconds each time, but I cleaned it out thoroughly and it didn't happen again. (Noise was from PSU, I think) Any ideas people?