Can't work Windows Defender in my Laptop windows 8.1 64 bit.

I am using Windows 8.1-64bit, for this, I am using Windows Defender as an Antivirus. When I open windows defeder It showing Message like " This app turned off by group Policy" and also shwoing, system have a other Antivirus. But I thoughly Checked out my system, there is no such type of Antivirus. So please Help me out. I don't want to install any other Antivirus into my system. Thank you....

Can't work Windows Defender in my Laptop windows 8.1 64 bit.