I try to installed a new after market stereo on.

I try to installed a new after market stereo on my expedition I did and it wpork fine for about 2 weeks. But a couple of days ago I smell a burning smell coming from the stereo I remove it to check it and it seems fine I re installed it and it did not wanna turn on I thought it was the stereo so I try a diferent one but nothing it seems to be receiving power because they iluminate when the lights come on. But it doesnt play or turn on and the stock multiple cd changer doesnt work either is it somethinf wit the electrical problem or a fuse or what could it be?