Car stereo not working?

[jtflautist]

Hi everybody, I tried asking somebody to check the engine light on my car, they accidentally jumped the wrong cable which seems to have stopped my sony car stereo from working now. I checked the radio fuse and fuse behind the stereo and they all look fine. I am still able to eject and insert a CD into the system so that means that power is getting to it right? Is there a reason why the head unit doesn't come on?

also Is it possible to fry your cars wiring with this mistake? But isn't that what the fuses are for? Is it just my head unit?

thanks in advance!