Hi,
I recommend you to login in safe mode by pressing F8 when you turn on your system. Select Safe Mode with networking and go to
http://www.trendmicro.com/hc_intro/default.asp to run a full scan, it's free and could be very helpful... Also I suggest to get rid of Norton and get a useful antivirus. Avast is one of them, free for Home users... Hope this help