I cannot say enough against Norton! Everything I have ever used that was Norton has caused one problem or another. One was when I could not access my C drive after it had done it's work. Lost all my data.
Problem to seems to be that Norton's stuff consistently finds problems and promptly get itself stuffed on how to deal with it.
Leave Norton OFF your computer is the best idea. Keep your disk healthy by using its own disk clean-up and as the wise Spanners says let de-frag do its great job, then let Scandisk do a 'thorough' through the night.
Next morning you will find it a pleasure to use your pooter again.
Some of the best utils and tools are the ones you can download for free. But......MS have thought about how to DIY quite well in my view so always try their way first.