Greetings... Preliminary: A short while ago I built my friend a new computer system. This system is VERY close to my own in hardware and software. I have been working with computers for more than 20 years, and I have a small hobby-business of building/working on PCs and related software. The problem I am having with his system started about the time that I built the system, and has lasted through various hardware/software changes. The Problem After using his computer for awhile, when he goes to Shut Down (to turn it off), it will sometimes shut the "system" off (HDDs/OS?) but will remain powered on. This happens randomly without any sort of pattern I have been able to discern so far. I have Googled the heck out this issue, but it doesn't seem to be a well-known phenomanon. The Current System ASUS M2N32-SLI Deluxe Wi-Fi MoBo Athlon64 X2 6000+ CPU Corsair XMS2 2GB PC6400 DDR2 (2x1GB) Dual Channel RAM Kit 2 x eVGA 8800GT 512MB Graphics cards in SLI (latest non-BETA Drivers) Soundblaster X-Fi Xtreme Music PCI Card LG GSA-H55N SATA DVD Super Multi Burner LG GSA-4163B IDE DVD Super Multi Burner 3.5" Floppy Drive WD 250GB SATA2 HDD (Primary, with WindowsXP Home SP2) *Dual Boot* WD 250GB SATA2 HDD (Secondary, with WindowsXP Pro SP2)*Dual Boot* PC Power&Cooling Silencer750 750W Quad-SLI ATX 2.0 PSU Silverstone TJ-07 Tower Case with LOTS of air cooling All latest drivers and DirectX AVG Anti-Virus Logitech G15 Gaming Keyboard (USB) Logitech MX1000 Wireless Mouse (PS/2) Wireless = DISABLED, Internet/Network via onboard GigaLAN What I Have Tried > Current Video Cards replacing OCZ 8800GTX 768MB > Replaced second SATA DVD Burner with IDE Burner > Current PSU replacing Enermax Liberty 620W PSU > Reformatted and Reinstalled Windows on both drives > Removed X-Fi, tried onboard sound and NO sound at all > Disabled Firewire > Reinstalled several drivers > Disabled nVidia Driver Helper Service > Changed LAN Ports > Changed LAN Cables/Router/Connection > Both HDDs are new & Replacements > Shutting Down Hot & Cold (happens under both circumstances) > Nothing in Error Logs > Used Tweak Manager to enable "Power Down After Shutdown" Reg Entry > Checked all Power Management settings in BIOS and Windows > Have tried a number fo other "little things" What I Have NOT Tried > Using another Keyboard & Mouse (Trying that next) > Replacing MoBo, RAM and/or CPU (Can't really dot his unless I know that's the problem) > Replacing PSU (This is the second one we tried, I can't believe we'd have that bad of luck > Reinstalling bare Windows again, then see if it happens with just the OS and no other software (I'm sure it happened on my last reinstall though). > Adding Ethernet card (no available slot without pulling X-Fi) > Updating BIOS (There's only one newer and it says it's only for CPU support) I'm not sure what else I can do... I'm leaning towards this being a hardware issue, but I just can't tell him to start replacing key parts without at least an idea of what's wrong. Keep in mind, other than the video cards (I have a 8800 Ultra), SATA Burner (mine are both IDE), PSU (mine is a Silverstone 850w) and wireless mouse (I have a Logitech G5), we have virtually the same systems... I have the same XP Pro install on my main HDD that he has on his Secondary HDD (the one I am using to troubleshoot). Other than the AV and his use of iTunes we have nearly identical software as well... and I have NO issues. He is a friend, but I am not about to start pulling my system apart to provide "test" parts for his MoBo, CPU and RAM... I need some more direction as to the problem. If anyone could offer some concrete advice/assistance I'd truly appreciate it. Thanks!