No PC Signal. When I turn on my TV it says No PC signal then counts down from 10 and goes on

Question

When I turn on my TV it says No PC signal then counts down from 10 and goes on standby. It wont let me change the source or bring up the menu. When I hook up my PC to it the image is displayed but I still cannot change the source. Can anyone help me asap?My tv started this "no PC signal" today after I unplugged it and mounted it to the wall. It was working fine 20 min. earlier. Any solutions on what to do next??