Windows slow down after installing AV !

I see that you have received an excellent answer to your post in the Norton Community You are in very good hands with AllenM.

Windows repair doesn't serve the purpose. It only rewrites the Windows system files. But since you have used the removal tool, I reckon it should be gone from the registry.
I would suggest you to use,
1. Anti-malwarebytes.
2. Super anti spyware.
These tools are used by virus removal techs... run a full system scan and then delete all the treats found.
Also, use the revo uninstaller to delete any programs... it reduces the hassle of manual removal of any registry keys..
NB: run the malware removal tool in safe mode. These tools are not complicated as Norton power eraser.

I hope it helps...