Hi Phil.c, lets start over and try to help fix this slow PC. Here is what I recommend.
1) Use anti-virus software, I don't use a full security suite as this can slow down your PC, check to see if your Norton is set to scan at startup, if so stop it, there is no need to scan at startup but do regular scans at sheduled times.
My recommendation for a anti-virus software and not a full security suite ,nod32 ESET NOD32 Antivirus Home/SOHO Edition for Windows
Free anti-virus is MS security essentials
2) Uninstall old programs that are no longer required as these may be running at startup.
3) Turn off programs that try to check for updates every week ect such as:
Itunes, Google updater, Adobe products, Apple software, Roxio, Windows Live. BUT if you do this you will need to check for updates often as this is important for security.
4) Check for updates for your PC drivers & Microsoft security upadates regularly. You will need to browse to your PC's manufacturers web site to check and you will need you PC/Laptops model number. If you are not sure how to find it try this page.
5) Clean your PC for dust, this can cause overheating and performance degradation.
How to clean a laptop http://www.youtube.com/watch?v=0yyEV...feature=fvwrel
Only do the above if your are comfortable removing covers from your computer, if not take it to a repair shop
6) Run disk cleanup often this helps remove old files that are not required on your PC.
Disk clean up XP:http://support.microsoft.com/kb/310312
Disk Cleanup Vista: http://windows.microsoft.com/en-AU/w...g-Disk-Cleanup
Disk Cleanup 7: http://windows.microsoft.com/en-US/w...g-Disk-Cleanup
7) Defrag regularly, I know some of you already do this but I need to add it.
Defrag XP: http://support.microsoft.com/kb/314848
Defrag Vista: http://windows.microsoft.com/en-AU/w...your-hard-disk
Defrag 7: http://windows.microsoft.com/en-US/w...your-hard-disk
8) Keep your internet browser up to date, firefox, ie ect release new versions but be warned that these can be in beta format so there may be issues with new releases.
Google Chrome: http://www.makeuseof.com/tag/8-cool-...google-chrome/
9) Review your hardware, such as memory, hard drives and video cards. As more software, updates and service packs are released you will need to review harware requirements. But if you are running a minimum amount of memory e.g. 512 on Xp, 1 GB on Vista and Windows 7, a memory upgrade is a good place to start.
This is not a comprehensive tutorial but more of a basic overview, If I have missed something please feel free to add it as I may put this in the tutorials section.