Why can't I double tap to wake up my Lumia 520 anymore?

[WPCentral Question]

why cant i double tap to wake up my lumia 520 anymore?

i cant double tap my screen to wake my lumia520 any more.i used to do this and i enjoyed it but my phone just couldn't respond anymore.what could the problem be and how can i go about it?

 

[xandros9]

Re: why cant i double tap to wake up my lumia 520 anymore?

obvious thing to check: make sure its switched on

its safe to assume it functions fine with the power button?
can you make a call where the display would turn on and off appropriately (off when top part covered, on when not)