OK. I'm running XP Pro. My machine has run fine for a long time. I have a 20 gigger as a primary drive and a 40 gigger for backup purposes. I has another 40 lying around, formatted and partitioned, so I decided to install it and throw some stuff on it. I swapped the 2 40-gig HDDs and powered up. It POSTed fine. When XP booted up, it was doing the autodetect and auto install. It recognized the drive as a WD 40 gig, it recognized it as a hard disk drive, but then immediately after that, it rebooted. I tried it again with the same results. So I swapped the drives and am getting the error still... Coincidentally, I have a Sony DSC-S70 DigCam. I plugged it into the USB port and turned it on to transfer some photos. The machine recognized it as a Sony DSCS70, recognized it as a removable HDD then rebooted!!! So I'm guessing it has something to do with the drivers for the HDD or something like it. I actually have no clue what it could be. Could someone PLEASE!!!! shed some light on this for me. I've checked the MS Knowledge base but to no avail. Any help would be greatly appreciated.