Run a virus scan. If you have a virus, format and start over, thats the only way to really get rid of it.

See if it happens when you try to boot into safe mode.  If not, disable your startup items.

From Run, type "msconfig" > go to your startup tab, disable everything, apply.  Then reboot in normal mode and run an AV scan.  You can also try a scan while in safe mode for good results.

Norton? IMHO Its the worst antivirus in the world!! I would rather run a computer w/o an antivirus than install Norton 

   Well, if your running norton, you are running a virus!    LMAO  * ^_^ *        AAr , I always do a scan in safe mode as already stated, that way the infected program ( hopefully ) isn't running, therefore it will not be able to mask , or disguise itself.

I concur with DL. 

I'm sorry for your loss.. hehe,
Is norton aware of this?!

we are on the same boat.. hehehe 

haha...
Norton SUcks, and installing it takes foreever GEEZ! 

which i actually did on my old dell...i backed up my important stuff and said bye bye nortons...then inserted the windows disc and rebooted.... damn nortons....

no...
Norton coudn't care less..

They actually care a lot less.. hehehe 

uninstall the antivirus , do restore to prior the installation

First of all as many others suggested I would get rid of  Norton Anti-Virus and Norton Fk up the Works. Cause #1 Norton Programs get into everything and use too much of your Systems Resources which is one thing that could be making your Computer run Slow.
#2 Norton Programs seem to deteriorate over time and completely screw things up at some point. I used to run Norton until I used some Computer Diagnostics Programs that identified Norton as the PROBLEM with my Computer. Since that time Norton has caused my Sister's Computer to get to the point where it would not even Boot anymore. And now I have a Room mate with the exact same problem caused by Norton Software.

Now as  far as what to do about your System, you have two Choices, either you can play around trying to Repair the Software or Fix your Windows Problems that were Created by the Virus (If you know how to do that) if you do not know how to do that the next easiest thing to do is Format your Hard Drive and Start over.
I Recommend using a Mcafee Rescue Disk to check your Hard Drive Track Zero or enable your Bios Virus Detection if you know how to do that. Boot with a Mcafee Rescue Disk or other Anti-Virus Rescue Disk Preferably NOT Norton.
Some Viruses such as the NYB Virus can embed themselves in Track Zero of your Hard Drive or even MOVE Track Zero so even if you Format the Hard Drive the Virus is still there and will just mess up you computer again after you re-install everything.

Another Possible Soultion is to Format your Hard Drive then Download a Copy of Linux at Linux.com it's Free and it is getting easier and easier to use, and rapidly getting to the point where it may just over take Windows very soon because there are so many people envolved in making it better and better everyday. I would say give it try.
There are many Viruses out there that are designed to only work on Windows, if you Download Linux then the Virus can't work anymore. But it is not an Absolute Protection against ALL Viruses because many Viruses are Multi-Platform capable.

Back to the main issue, you really only have two Options, either you know how to Fix Windows or you don't, if you don't know how to Fix Windows, then you need to Format your Hard Drive and Re-install Windows. Hopefully you know how to do that.
You just put the Windows CD in your CD Drive and Turn your Computer Off. When you Turn it back on, Click to Install Windows, and Select DO NOT SAVE SYSTEM FILES otherwise you are saving the Virus. Do not select the Repair option or you will also Save the Virus.

Good Luck,