It could be heat related and from the description you give of your problem (no error code) I would guess you need to disable Auto Restart to see an error code.
Control panel > System > Advanced Tab > Start Up and Recovery > Settings button > System Failure > Uncheck Automatically Restart.
By doing this you will now see an error code next time your pc shuts itself off. Write down the error code and post it back here.
Also you can check your events log - Right click My Computer > select Manage > expand Event Viewer > select System
Look for errors and if you don't understand what the error is displayed Google it.
Charchris mine look pretty much like yours inside even after i scaned for virus and found 2 trojan that it supposably have deleted but after i shut off and restarted it now still try to restart and shut off and retry and so on wiht out restarting completely
Dlligaf i have look for error messages but found none, it now still try to restart and shut off and retry and so on wiht out restarting completely i think i will bring it to the repare shop, hope it wont cost to much and will not loose any data
Actally I posted in the wrong thread, sorry xD
Sometimes they don't tell you if they reformat, ask them if they will before you take it in to teh repair shop.