Not a solution, but if you run Norton System Doctor, my suggestion is simply turn it off from startup. It is supposed to monitor your computer and do things such as warn you about system running out of resources, disk space, disk fragmentation and so on. First of all, you don't need it to tell you about these things. You would know anyway. Second, even if you find it of some use, it's not worth the resources it hogs. I'm not a Norton basher, as I use Norton SystemWorks myself. But I do find SystemDoctor a waste of time. I used to disable it, but now I simply exlude it during installation.
Go into Norton's configuration options and tick SystemDoctor off from startup programs.
If you're not prepared to turn it off, then hopefully someone can give you a suggestion for resolving the problem.
Check that you have enough memory. If memory is short, tick off other unnecessary Startup applications in msconfig.