Hi Nardi
I also had exactly the same prob today, I did want to spend too long time to solve, so I came out with this solution:
I went to BIOS setup
to Power Up
there was option like POWER LOSS RESTART I chose DISABLE.
I\'m sorry i cannot remember exact name of the menus,have only one PC, what I know is that it should be in the same place as the place you configure how to turn on the computer using Mouse.Keyboard.Netcard. etc.
I did this because.....
I suppose that there is some miscommunication between OS and Hardware. The prob is OS couldn\'t tell the Hardware that it is OFF / it just decide to shut off the computer as a result Hardware thinks that there was power loss then it will restart/reboot computer immediately.
This should have been caused by badly developed software, If you have time you can try to find it by unistalling one software at a time and then try to restart untill you can find the problematic software.
meV