It is unwise to run more than one anti-virus program, and particularly, Norton and AVG do not like each other.
Certainly with AVG, I have had no problems running Spybot, Spyware Blaster, Spyguard, Adaware, and Zone Alarm together.
It may be worth looking at your Start Up programs, and disabling them all. Now boot-up and see if there is still a problem. If not, add one program at a time to your start up folder, testing each time, to see if you still have a stable system. Once it becomes unstable, you have very likely identified the problem program and can then try to do something about it. Either scrap it altogether, or see if it is a known problem and (maybe) a fix exists.
If (after disabling the start up programs) you still have an unstable system, then it is the system itself, and you have to look at different solutions to the problem. This may involve up-dated drivers and suchlike, but more on that if it becomes necessary. It would also be prudent, to run a system anti-virus scan (with the latest definitions) in case this is the result of a trojan or worm for example.
If I had to take a bet on where the problem lay, I would pick Kazaa, as in my experience, this program causes more problems than enough!