Windows Defender in Windows 8.1 Will Not Turn On

I have the same problem

Have Dell all in one Inspiron 2350 with Windows 8.1 factory installed. Purchased March 2015. Also McAfee 36 month subscription. Today on turning on computer (first time since June 15 - its now June 19) getting errors the same as reported above. It seems that neither McAfee nor Windows Defender are turned on. 

Have done all suggested above and still get the error from the action center. When I attempt to turn on Spyware and unwanted software protect, virus protection the Action center reports :This App will not run. Windows did not trust this app because its identity can't be verified.

What's going on?

Since you have a 3 year McAfee subscription, you should be seeking assistance from McAfee (or Dell) support. With McAfee installed, Defender will be off.

http://service.mcafee.com/default.aspx

https://community.mcafee.com/community/home

http://www.dell.com/support/home/us/en/04?c=&l=&s=bsd

-steve

I have the same problem - I tried both of your methods & received errors - unable to send screen shots due to word count

You can send a screenshot of your computer by pressing Prt Scr key on your keyboard (And/ or Sys Rq) and it will take a screenshot of your screen. Ctrl + V will paste it into the text.

Rajesh, your suggestions on how to turn the Windows Defender on are fine for and should work, but when I bought my HP Pavilion, it came with McFee installed. I don´t like it so I uninstalled and I thought that was just a matter of going to the Action Center and turn on the Windows Defender. I click on activate, but nothing happens. After following all the procedures, the damn thing still does not start. So I had to install Avast (another antivírus). I cannot understand why everything worked so beautifully on Windows 7, but now on Windows 8.1 is a real disaster. Microsoft would do so much better as a company if they stopped trying to be like Apple and thought what is that a Microsoft user expect. Oh well, what can I expect from Microsoft?

when I bought my HP Pavilion, it came with McFee installed. I don´t like it so I uninstalled       

Have you ever run the McAfee Consumer Products Removal Tool?