If I were you I would eliminate the possibility of a software problem before swapping your mainboard or processor (which is the only way to test such hardware at home).
Option One is to do a low level format on your drive which will clean everything off and give you a fresh start for doing a high level format with your windows CD - if you don't have a windows CD but a restore set-up, then this may not be the right way to go.
However, if you have a windows CD then download the drive manufacturer's diagnostic utility from their website (usually goes onto a floppy) and use it to set your drive to zeros - this will remove everything, so do back-up anything you want to keep. Once you have installed windows you will need to install your mainboard and graphic drivers, etc. If you do restarts as you load each driver you should be able to spot any problematic driver clashes.
If you're not sure which hard drive you have, you can use this to find out:-
Option Two is to do a 'repair install' of windows which should leave your data in place (but consequently is not so thorough for troubleshooting the possibility of a software problem), however, it will mean you can try out the system without SP2 and with some assurance that your windows files are in tact and working as they should:-
With either option I would suggest leaving Norton off and installing AVG and Microsoft's anti-spyware program along with Adaware-SE and Spybot - all free and all well tried and tested software which does the job they were designed to do.