My cousin messed up her computer and is now expecting me to fix it. explorer.exe is consuming 99% of the processor resources starting a few moments after the OS loads and will not stop. Killing the process and restarting it is effective for about a minute then the explorer.exe process again runs out of control. It is the same situation when booting into safe mode under her and the administrators account. Norton antivirus is installed and up to date however it is unable to find anything in full system scans. I tried using checkpoint to revert the system back to a previous point however going back several months prior to the issue appearing it advises that their have been no changes to the system. I have used an adware removal tool I cant remember which one at the moment and after updating its definitions and running a scan it did pick up some adware which was removed however the problem is still present. I am thinking that since the issue is present whether booting into safe mode or not, under multiple user accounts that explorer.exe has in some way been corrupted. Or could it be possible that this was the result of some kind of conflict between norton and explorer.exe? I am only throwing that in their because I am advised that the issue came about soon after norton being installed.
Let me know if you have any thoughts?

OS is windows XP home edition SP2 on what I think was a compaq laptop but cant remember the last part for sure as I dont have it sitting in front of me.