As oscer1 says, yes you need to uninstall McAfee, and the best way to do that is to use the tool that McAfee designed to do it rather than to use the onboard uninstaller that come with the program.
That's method 2 on this page ....
https://www.mcafee.com/support/?articleId=TS101331&page=shell&shell=article-view
Alternatively uninstall it using RevoUninstaller (free) ....
Revo Uninstaller Free .... I usually recommend the portable version.
If after uninstalling McAfee you find that Windows Security has not enabled, then get back to me, as it means there are still remnants of McAfee left on your machine, and I can help you to remove them. This is not usually necessary, but sometimes it is.