I built a new rig about a week or so ago: Q6600 G0 Asus P5KC 2 GB OCZ 1066 DDR2-8500 8800GT 512MB Sounblaster Audigy 4 2 x SATA HDD, 1 x IDE HDD, 1 x IDE DVD-RW Antec Smartpower 500W PSU Running Windows XP SP2 I bought and have been playing Bioshock (through Steam) at high settings with no problems at all (more than 15 hours racked up in this game with extended 5 hour + gaming sessions no problem). Bought NWN2: Mask of the Betrayer and COD4 as well a few days ago, and installed both earlier. However, when I try to play them my PC just reboots of its own accord. This happens at about 2-3 minutes into NWN2MOB, and with COD4 it always happens at almost the exact same point during the introductory sequence whilst the main game is loading. Portal runs okay as well as Bioshock. Given this pattern, I suspected a Securom problem, but I found it happens with Oblivion as well - again after about 2 minutes of game time as with NWN2. (I also tried a no-DVD crack for COD4 to see if that helped, but it didn't make any difference) I also found that the HL2 Lost Coast video stress test causes a reboot as well. So... how do I diagnose and correct this issue? Why does Bioshock run so well for so long whilst a less taxing game like NWN2 causes a reboot so soon, and COD4 won't even get past the introductory loading sequence? I am stumped. Usual suspects for me would be: PSU - but it's a quality brand, with 37A on the 12V rail - and Bioshock runs fine? RAM - but Prime, Orthos and Memtest run okay (Prime for 10 hours blending, Memtest I've run for 11 hours without errors) Gfx card - I've read about some problems with the 8800GTs, and have tried underclocking everything on the card (though my temps are fine on it anyway) and, again, Bioshock runs perfectly! I've restored my BIOS to default settings, turned off RAM transaction booster, onboard audio, PCI memory mapping, and other potentially destabilising settings, but still no joy. I've also got the latest chipset, gfx and sond drivers installed. I've tried swapping my memory sticks around, using one at a time, and changing the slots they use. I have no other PCI-E gfx cards to test with, nor a spare PSU. What are my next moves? Help! Please! I have automatic restarts disabled in system settings as well.