The Reason that McAfee turns off again could be an infection. Please check what is the last update on the product. You could check that by
Click on 'Navigation' then select 'About' , Were you can find the Last update Date of Virus Scan Plus.
Also would like you to check the host file on computer, which you can find in location C:\Windows\System32\drivers\etc\host
You have to right click on the host file , click 'open with' option and select notepad to open it. It should be like
If Host has any changes then there might be chances of Infection.
You may try uninstalling and reinstalling Mcafee. The link bellow will be useful in doing so.
If you have hard time fixing this issue you may get help from our technical support team, you may click on 'Usefull Links' on top of the page and select 'Technical Support'. There you may find free chat and e-mail option.
Thanks and Regards,
Krishna Nandan Singh
This document from McAfee may assist you in dealing with your issue. May I suggest you try to follow some of the recommendations here to troubleshoot the cause.
If problems persist, Technical Support Chat may be able to remote connect into your computer to see if they can find anything that may causing the problem. You will need to give them permission to do so and they have many more tools available than we do here on the forum. Chat can be reached via Useful Links at the top of this page under Technical Support.