Make sure Windows 10 is up to date.
Uninstall ALL McAfee listed in Control Panel > Programs and Features
Then turn off Fast Startup as per this tutorial. Don't worry, it makes little difference to start-up.
Run a freshly downloaded MCPR and reboot.
Go to your account page and reinstall from there.
Fast start-up prevents Windows from properly rebooting, this often fouls up the system.
Ok, so I did directly as you stated. Now when I try to install it gives me a new notification. I restarted my pc right after closing out of this box. I decided to reattempt downloading the Mcafee Installer after the restart and got the same notification being " You must restart your computer before reinstalling McAfee products."
I believe your machine is not rebooting. There's a world of difference between restarting and rebooting. Did you check the Fast Startup and made sure the settings were saved?
If so and it still gives that then you will have to call (or chat online) Technical Support, it's free of charge.
Depending on your location it may only be open during working hours.
I have exactly the same problem. Have found no solution that works.. i'll let you know if i find something, please do the same for me. I am sure others are looking for help.
Contact Technical Support as advised earlier with the link to it shown there.