Spyware? Help!!

Last night I received pop-up messages on the bottom of my screen saying that my computer was being attacked and files were infected.  It then asked if i wanted to purchase antispyware or stay unprotected.  It looked shady so I clicked no and stay unprotected.  However, it keeps bringing up some antispy-guide site trying to get me to purchase their product.  Every time I try to get on the internet it says the page may be harmful and to buy this product. 

 

How do I get rid of this thing?  Everything I click on brings up a box saying that the file is infected and to purchase antispyware.  I ran a full scan with norton but it came back clean.  There is also a small green shield/check in the bottom right corner that will not go away and when clicked on is the antispyware page. 

 

Is my computer really that messed up?  Or is this something that can be fixed?  The problem I'm having is that this virus (or whatever it is) won't let me get on the internet to download anything to try and fix it. 

Any help would be appreciated.

 

Thanks