Restarts instead of shutsdown.

Currently using an Abit AN8-SLi with AMD64 3200 300+ GB harddrive space 1GB RAM. The problem is on a fresh install of XP pro, only things installed are current drivers, current updates and service pack 2. The system tends to restart instead of shutdown when instructed to do so. Just wondering if we should reinstall drivers or remove update patches to see where the problem lies. The system worked beautifully before we wiped the HD and started over.