You have at least one problem with malware (virus, spyware, hijacker and so on...). Please download and run Spybot and AdAware SE. In Spybot fix items checked in RED... In AdAware fix whatever it indicates is bad... Also, it is a good idea to run an online virus scan, there are links to 2 of them at the bottom of my post. Then you need to run HijackThis and post a log to clean out whatever is left.
To run HJT, extract it to a permanent folder such as one you create like C:\HJT. Close all open windows and browsers and make sure that all programs are enabled if you use msconfig. Run it and Scan, then Save the log. When the log window appears, Right click to Copy it, open your browser and come here to Paste the entire log. Do not make any changes until it is checked since most items are either benign or essential to the computer.