Hi hk415, welcome to TSF
From your description it looks like your computer is infected. Don't click on any popups or adverts or offers for anti-spyware software.
HiJackThis is a scanning tool that security analysts use to detect malware, hijack attempts, etc. It's not for beginners so I recommend that you follow the instructions
here (5 pages) and then post all the requested logs in a new thread
here for our analysts to look at. If you have any trouble running any of the scans, leave them and move onto the next.
The security forum is always busy, so please be patient and you will receive a reply as soon as possible. If you go to Thread Tools > Subscribe at the top of your new thread you will receive an email as soon as a reply is posted.