Rather than downloading shit on the net, or having some online program scan your pc , just go buy ad-aware plus. When you download, or use online software, you can't tell if whether or not it's a clean file or not. Therefore, you're taking a HUGE risk there !! Sometimes you will get a box that pops up saying something like: "Do you really want to save this file?" . When you click "yes" , what you don't know is that lt is an infected file, and since you've allowed it to run on your computer, it will find a file to locate itself within your registry. And sometimes you can't get it out. Next thing you know your pc is fucked up and doing weird things, or showing odd behavior. That whole "shutting down" by itself thing kinda sounds like a worm of some sort. I know last year the "Blaster Worm" did this to alot of people. It actually got me twice until I found a way to beat that sucker. Let me ask you this, right before it shuts down, does a little box pop up and say "Windows is shutting down in 10..9..8..7..6..5..4..3..2..1.." And then turn off?