Try to reboot into Safe Mode and there you could start System Restore and go back to before this started.
If successful start again by uninstalling all McAfee products via Control Panel > Programs and Features.
Then run the Consumer Product Removal Tool downloadable HERE.
Go to your online account and install your new product (or install from wherever you are obtaining the new one).
What is the Operating system that you have installed in your computer and what product of Mcafee have been installed ?
windows 7 and i think it was total protection
Alright in windows 7 OS system you can try running MCPR first which should remove the MCafee product, if it fails you can reboot the computer in Active directory repair mode and remove the product.
How to get into AD repair mode:
1) Open RUN window (windows key + R combination will launch Run window)
2) type msconfig in the run window
3) systemm configuration window will open in which you need to select Boot (second tab)
4) Check the Safe mode option and select Active directory repair mode.
5) click on Ok and restart the computer.
6) Computer will reboot in AD repair mode where you can uninstall the product.
7) after uninstall you need to launch msconfig again and uncheck the safe mode option under Boot tab to load the computer in normal mode.
If you are sure about Registry, then you can take a registry back up and delete the Mcafee registry key under
HKEY LOCAL MACHINE\SOFTWARE\MCAFEE (You need to delete only the MCAfee key and not other keys
Simply restart the computer to safe mode (tap "F8 " on boot)
Uninstall McAfee from programs and features
Reboot the computer(Normal Mode) and run the McAfee Consumer Product Removal Tool using the link: http://mcaf.ee/mcpr
After clean up you would be prompted to Restart the computer.
Now install the version of McAfee you want.
Post back the outcome of the steps.