Cannot select the internet button

I can sign onto my system.  I can even go into yahoo messenger.  But I cannot access the internet.  After I select the internet button, my screen acts like it is trying to download the screen.  Then it locks up and just stops.

What's going on?  How do I fix it.  I ran Norton Antivirus and it says I have 9 potential threats.  It will not delete them. 

thanks,