Clean out you browser's temp files and cookies. Use a free program such CCleaner as well.
If you are a novice and not comfortable with your knowledge of how to download or limited experience, try to scan computer with Norton free virus detection and security scan. (Do one at a time. I'd suggest virus scan first)
You will have to download Norton software. This is all free. Make sure you read the prompts before your select. The scans take a while depending on the size of your hard drive so you may want to run when going to bed and leaving for work.
http://security.symantec.com/sscv6/home.asp?langid=ie&venid=sym&plfid=23&pkj=VOYJZMRMKBWGZKMRYLL
If you have some abilities with your computer, go to majorgeeks.com. then click top freeware picks on right side of page. They break down free applications and what they do. Follow recommendation for # of programs to install that are similar. Some will do the same things so try to do a little reading b4 installing.
I'd recommend installing Malwarebytes and Super Antispyware. If you don't have a firewall look at Comodo Firewall or Zone Alarm.
I would also download a program named Erunt. This app will backup your registry every time you bootup. If there is a problem, you can go back to how your registry was-somewhat like Restore. I never had any luck with Windows Restore.
Check to make sure your antivirus is up to date. It amazes me when I go to stores like Bestbuy that people pay for antivirus software. There are a lot of free versions that are just as good. AVG and Avast are well known.
If you need a name brand, check with your internet provider. A lot of providers offer Norton or Mcafee free for their customers. You have to sign in to their site with your e-mail adress they offer. Google the name of your provider and free antivirus to see if you have this option.
Make sure, if you downloaded the Norton scan software, to uninstall and remove any and all components of Norton or any other antivirus software before you install another antivirus. There is the potential of clashing if Norton is still present and you install Macafee or AVG software.
To run a thorough scan, I'd suggest booting in safe mode then run the scans. This will allow scanners to check more services that are not running in background.
Hope this helps