I have installed Windows 7 Pro on a pc last Saturday and had this trouble so I did another fresh reinstall figuring the first time it didn't install properly.
So I am done the installing, put my AVG antivirus on it and now I am putting the updates on it again and the same problem again. It will install updates but if it takes a while checking for them which sometimes it does the the computer just shuts down all on it's own. now when I restart it I have to select the normal start up and so on.
If I turn windows update off completely then there is no problem, the computer will stay on for days. So I know it's got something to do with windows update.
I use TPlink internet adapter stick for my wireless internet on it if that makes a difference.
Not much else on it right now except for Firefox, IE...
Any suggestions would be appreciated...
AMD Athlon 64 x2 Dual Cor Processor 3600+ 1.90ghz
Not the most powerful computer but it's for the wife and all she does is facebook, email and surf the net. She doesn't even need to play videos on it anymore as I got her an android box for that