First thing first, install licensed Anti-Virus software on your computer. Norton, Kaspersky or any anti virus that can be available to you. Then you can run a cleaner on your computer to remove temporary internet files, cookies, history, etc and fix registry as well. I can give you this website to download CCleaner, I'm using this in our office to maintain computers.

http://download.cnet.com/ccleaner/

You can also try installing different browser like firefox and google chrome.

http://download.cnet.com/mozilla-firefox/
http://download.cnet.com/Google-Chrome/3000-2356_4-10881381.html

Good luck!!