problem downloads

hi,i am having problems here,i have had some advice from a couple of guy's(thanx) regarding viruses/trojans etc,the problem being my pc is slowing down dramatically,also internet explorer on desktop does not open unless i click run as........ security websites wont let me have an online scan,any anti virus downloads don't happen,infact anything i try to download doesn't work i get the download dialog box to open then it says file downloading although there is no movement in the status bar then after a minute or so i get the message internet explorer cannot download file,i am using windows xp,i updated my norton anti virus 2003 AFTER i realised there was a problem,as a novice any advice is much appreciated.

Scotty,
you probably should have put this with your original post. Than everyone would know the entire problem. It might help in the solution to your problem.
For those who don't know, scotty's original thread is here