Hi... I recently built a new PC for my father, a Pentium D machine using all brand-new parts from Tiger Direct. The machine occasionally reboots at random, but I've really noticed the problem more when running a virus scan or a disk cleanup. When the problem first occurred, I did notice a slight grinding noise coming from the CPU fan, so I replaced that on warranty, and I haven't heard the noise yet. CPU temp is normal, roughly 38-40C idle... There's really no extended heavy CPU use, as my parents don't do any gaming, just MS Office, Quicken, web & email... My gut reaction is a power issue, because I'm running the Pentium D 830 with 1GB DDR5400, (1) Seagate 250GB PATA HD, (1) Hitachi 20GB EIDE HD, (1) ATAPI DVD+/-RW, (1) ATAPI DVD-ROM, (2) 120mm ball bearing case fans, 1 input on back of case, 1 output on side panel, almost directly above cpu fan. The PSU currently in the machine is only 400W. I'm considering upgrading it to a 600W, but I'd really rather not unless the chance of it correcting the problem is high enough. I've already tried disconnecting 1 HD and 1 DVD-ROM, and still ran into the problem. Any advice would be greatly appreciated.