Sounds like your PC could be loaded down with malware. It's not slow, it's just busy being used by various criminal types to spam people with misspelled viagra ads and launch distributed denial of service attacks, maybe searching for passwords and tax records, that sort of fun.

Anyway, you need to get some anti-spyware programs and some more antivirus software, and scan your computer thoroughly.

Note, you should probably go find your 'hosts' file in C:\WINDOWS\SYSTEM32\DRIVERS\ETC and rename it to something else. It's one likely place that malware will redirect you to additional malware from. You can view it if you like. If the only thing besides lines that start with a '#' is a single line about 'localhost', it's fine. Then go into your 'Internet Settings', find the connection settings and make sure you're not connected through a proxy (at least, not a proxy that YOU didn't intend to connect through), or you will again find that links to anti-spyware and antivirus software just gets you more spyware installations, or placebos that behave like they're scanning your computer for malware that are just wasting your time.

http://free.grisoft.com/
http://www.safer-networking.org/en/index.html
(and more people will chime in with their own favorites, soon)

If installing and running various malware scanning software doesn't fix it, try a 'Defragment' of your hard drive. Also very time-consuming.

If you're still stuck, then I'm afraid you might just have to back up your data files, music, pictures, etc. to an external drive, track down all of your OS/Rescue and software CDs and licenses and web/mail passwords and reinstall windows from scratch. Your computer will be nice and fast just like brand new... for a little while, until it gets filled with malware again.

DO NOT USE Internet Explorer. Use ANY other browser besides that. Firefox, Opera, whatever. ANYTHING but Internet Explorer to browse the web. Anything besides a Microsoft Mail client like 'Outlook' or 'Outlook Express' to handle your email. These are so chock full of exploited security holes that you may as well rename them the Microsoft Malware Installation Suite.

Yes Norton is a high wanting program and it slows down your computer but you had it before this started so you must try do a complete scan sometimes you or your computer can select quick scan and that will not detect all the harmful things.

Vlad