internet explorer problems

Hi,

I have recently noticed that when I use the quicklaunch button for internet explorer I get two webpages opening up instead of one. Also when I click on 'back' while I am on the internet, it takes me back two webpages instead of one. I also have difficulty in choosing from a drop down menu on the internet since the menu does not hold, I have to click on the button with a drop down menu several times to get it to hold so I can choose from it. I have also erased everything on my computer and restored it but the problem remains. My antivirus program isn't showing any problems and I have run diagnostics and everything is ok. I have a Dell Dimension E520 running Windows XP.
Any ideas on what is causing this and thanks