I also had this exact problem. The computer would operate with no issues during normal operation. When shutting down the software would shutdown correctly and then the system would power off. After 3-4 seconds the unit would power on again as if I pressed the power button. There are no errors or issues during boot-up or shutdown. I tried installing the newest BIOS firmware and then an older one - no change. I installed the newest drivers and utilities and checked for viruses - no change. I made sure BIOS settings referring to power management were turned off and Same for windows options. The problem was quit frustrating. One thing I did notice was the delay for power on seemed to equalled the BIOS change sequence. When the Bios setup was modified in a major way, such as the clock speeds being modified, the motherboard would power down the computer and then power it up again after a 3-4 second off time to activate the new settings. I contacted Gigabyte and asked their experts for a solution and they gave me a link to download the newest software driver for the SATA2 raid controller. This did not work either. I recalled an old trick we had to use on a brand name computer when all else failed - clear the CMOS! Yes this is the physical procedure where you have to move a jumper on the motherboard or press a button in my case. This is not the same as loading the fail safe defaults in the setup where it will not change what I consider that critical bit. After I cleared my CMOS the restart problem was resolved. This may not work for all but hopefully some will benefit.

I solved this problem on my Gigabyte Z68x-UD3R-B3 motherboard.

1. I updated the BIOS2. the problem still occurred so I changed the Power Management settings in the BIOS to:A. disable power on from PCI devicesB. disable power on from LANTheoretically both these settings shouldn't have mattered as I believe another setting had to be switched on for them to take any effect. But i no longer have the reboot problem when I shutdown.

Fortunately, it's easy to change this behavior. SelectStart,(StartthenRunin XP), typesysdm.cpl, and pressENTER. Click theAdvancedtab, and then click theSettingsbutton under 'Startup and Recovery' (as opposed to the other two Settings buttons on that tab). UncheckAutomatically restart.

Problem recognized: Wake on LAN

Right click "My Computer"Select "Properties"Go to "Hardware Device"Click "Device Manager"Select "Network Adapters"Select "Marvell Yukon .....PCI-Fast Ethernet Controller--> right click ---properties--->power management-->deselect "Allow the computer to turn off this device to save power"--->Go to "Advanced" tab--->put value off for "Wake from shut down" --->value none for "Wake up capabilities"press OK