Do the following and post back with the info so that we can narrow it down some:
Go to control panel/system/advanced tab/startup and recovery box/settings button/ sytem failure/ and then uncheck "restart on system failure" ( take the check out of automatically restart box ) , and then check the "Write a system event", and the "Admin alert" boxes (check "send admin alert") and the next time it randomly turns off, you should get a blue screen with white text, which will have code info. Write down the exac Stop Error Code and put that exact error into the google search box to see what info you get, and/or post that exact error here in this thread. (While you're waiting for a reply, you can put that error code in Google search, and in the MS Support Knowledge Base (KB) = http://support.microsoft.com/search/?adv=1
- to check it out.) http://support.microsoft.com/search/?adv=1
Also go to your device manager (devmgmt.msc) and check the properties and look for anything suspicious and check that the settings are where they should be.