Its probably just junked up with spyware primarily. IE does have a lot of holes in it that allow malicious items in there to slow down your pc.

Go Download Malware Bytes. Its a free spyware program that I have found to be great. It has gotten several spyware/viruses off of many computers i have worked on. If you or your dad, or anyone else have had problems with Antivirus 09, or Antivirus XP Pro (or any name sounding similar), you know its hard to get off the computer, plus it looks just like a normal window from Microsoft. This program will take care of it. Malware bytes will get almost everything malicious off your computer. You can also purchase the full version, but all that allows you to do is schedule scans. The free one you can just run yourself and it works great.

Go to this link:

http://www.download.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html

Click Download Now.

Once it downloads install the file and tell it to run the update first. Once it updates the definition file, you can either run a quick scan or a full scan. Quick scan will take between 3-15 minutes to run, depending how slow or junked up your computer may be. If the computer is real messed up, i suggest the Full Scan which will take probably about an hour to run. Once it runs and tells you how man items it found. View them and click remove selected.

Run this every week or two to help keep your computer cleaned up. Make sure when you run it again you always run the update first. This will help keep it updated against new Spyware.

If it is too junked up or possibly has a service running in the back ground that will not allow any spyware program to recognize anything. Then you may need to boot up in Safe mode and then run the program. Which you can do by clicking F8 (click it a few times to make sure it caught it) when the computer is first booting up, then selecting "boot up in Safe Mode with Networking" (so you can run the updates.).

If that still doesnt fix it, you will probably need to reload, or have someone who knows what they are doing to repair it.