Access Denied when trying to change msconfig

I have reprogrammed this computer four times trying to get rid of this error and it is still here. I am stumped and am hoping someone can help. Right now it has windows xp home, motherboard drivers, lan driver, first round of xp updates and Norton Internet Security. Motherboard is Gigabit A740G-M2+ and drivers are from them. I did take the installer for Norton from his backup files to install and it was after that when the problem started this time. I checked msconfig each time I made a change and again after restart. The microsoft updates came just before the norton install and I did not try msconfig at that time so it could be something in there I suppose. I reprogrammed another computer at the same time as this one (the first reprogram) and the other one had no problems but it does not have ATI products in it or Norton. There are three more computers here that all have Norton with no such issues. Any ideas?

 

When Norton messes up (or is installed where the Windows Registry already has underlying problems), it usually messes up big-time

I'd uninstall Norton, reboot a couple of times then run the Norton Removal Tool to ensure it's all gone.

Reboot again and test changing something in MSconfig, if it works ok, consider using Avast!/MSE and one of the free firewalls from the Top Freeware section. If the machine is for business use, you'll need to check whether those softwares are allowed to be used.