i am stumped on this one. when i tell windows to switch users the HDD powers down. when i log off and go into a new user it works fine. there is nothing in the bios to shutdown the HDD, and services have not been changed in xp, i hvae done a repair, a format and reinstall, is it possable that the motherboard is messed???? any other ideas, all tests were done in a controled enviroment and the PSU tests ok, and it was just with windows and updates no other software, no viruses or anything any ideas????