I would start by running a virus scan. If you don't have one, go to Trend Micro's Online scan here ->
http://housecall.trendmicro.com/hous...start_corp.asp
Then, install ad-aware located here ->
http://www.techwarelabs.com/download...ion=file&id=40
Make sure to update that before you run it.
Also, run msconfig and delete all of the extra stuff that you don't want starting up when you boot your computer.
While you are in there disable the "windows messaging service" to block those annoying windows messanger pop-ups.
That should take care of your problems.