|If you have any siblings, its always possible they connected a wireless keyboard (for the shortcuts to do such stunts) and mouse to your computer (which both work even while you have your own wired mouse/keyboard in the keyboard). But, if you don't, then that's probably not your problem. I just brought that up because I did it to my family once as a joke.|
My suggestions: download AVG Root-kit (finds and eliminated hidden viruses that most virus-scanners don't find), and run SpyBot to check for more prominent viruses. Ad-Aware is mainly for spyware and adware, not the worse stuff.
If those don't work in finding anything, I'd quickly call a professional to help because any (personal, important) files on your computer can easily be hijacked.