I've seen spyware/adware/malware cause this, even viruses. Bad memory can be a cause as well.
Try and download this. It's an awesome freeware pc maintenance package.
Refer to this page for the settings and instructions.
PM me with questions that you might encounter.
Are you having spyware problems? If so go here and follow the guide:
http://forum.ccleaner.com/index.php?showtopic=3505
Then post a hjt log here(directions in first link):
http://forum.ccleaner.com/index.php?showforum=12
Tarun
4
Nice job avoiding his question.
He PMed me for the answer and got it swiftly.