I would suggest downloading one of the free AV products, updating and running.
As you probably know some of these viruses prevent Norton from running.
My preferred one is Grisoft AVG here ;
http://free.grisoft.com/doc/1
An alternative is Avast here ;
http://www.avast.com/eng/avast_4_home.html
Both can be removed in their entirety after use unlike Norton !
It may also be worth downloading the new(ish) Windows Defender if you haven't already got it.