Walls, can you do me a favor and open up the Management window? (Right click My Computer > click Manage)
From there, go into the system and application logs (see attached screenshot). Look to see if you see any errors around the times of the shutdowns. If there's errors in there it'll tell you what caused the error. If you see no errors, then you might be looking at dying hardware or power supply.
If you have errors, please post a screenshot of the error and description. This will help me diagnose the issue
any update, WIZARD WALLS?!