You are only supposed to have a single antivirus software installed at any one time due to conflicts. MSE OR Norton, etc. You aslo should not uninstall them the conventional way (Control Panel Uninstall Programs), as it leaves remnants of the antivirus program. You should use an uninstaller tool (some antivirus companies create their own, or you might search for a community created one). Here is a thread about what people believe the "best" antivirus is: What's the Best Anti-virus?
- this is a good read to find out the benefits of one antivirus over another, and any additional security software that might be coupled with an antivirus, if interested. I've used MSE and recommended it for its compatability and lightness. I doubt it was the problem at all, honestly. But you by no means need to have it, as there are even better antiviruses out there, (I like MSE because it integrates with Windows very well) as you may read in the link I've provided. Everyone has a different opinion, it is for you to decide for yourself.
If you wanted to 'prove' if MSE was causing trouble, There is no need to install both, but you might have to do some time consuming work. I would recommend installing Ccleaner
and scanning the registry (be careful as without registry knowledge, even this trust-worthy program can delete something you might not want deleted). Look for any remnants of antivirus software from Norton and MSE (and any other that you may have installed in the past). Delete those files. I would recommend against deleting random things as, again, it may end up being something you might not want deleted. This is good practice anyway in case you wanted to install any other antivirus, as you decrease the chance of conflict. You can then uninstall Ccleaner. You could then reinstall MSE. If problems arise, then you know if is MSE causing the trouble after all.
- I don't know much about Norton Live, whether it is good or bad, or how well it performs with MSE. If you make any sort of choice, bear this in mind.