after uninstalling the old one and installing the new one, did you create an account for the mcafee antivirus? im pretty sure you would have done this but just checking?

Anyway i hope you didnt pay anything for it? ive been using avast free version for 2-3 years on my desktop and the misses laptop, never had a single issue with either of them, never pay for AV when the free ones work just aswell