I have a windows 7 box that I leave on all the time then remote into. Today I tried to remote into it and saw a desktop that was different from my usual desktop. I thought someone hacked in, so I tried to do a "shutdown /r" to kick them off. The screen froze and I was kicked off. I tried to remote in several times again and every time, I would get in then would get kicked off again. Something similar happened before and it was because someone logged in was sending out spam. I am not sure what happend this time.
How can I find out what happened and how can I tell if my computer is clean?