radio has power, but won't turn on.

I sold my friend a dual radio for $20 and it worked fine when it was in my truck. We put it in his, and you can hear the clicking through the speakers but it doesn't turn on. We put his factory radio in and it lights up but won't play music. We changed the radio fuse under the hood and the 5w fuse on the yellow wire. It is wired yellow to yellow, red to red, and black to black . it has me confused.

He said it worked for 5 minutes when he plugged it in the first time, and it is a 99 gmc 1500

You need a volt meter to make sure the red and yellow wires of the radio are really getting 12volts. When testing this, it is very important that you place the black meter lead to the chassis of the radio.

if you have a bad connection or a bad ground then it will cause a low voltage problem, it is also possible you have no power on the red wire which the radio uses as a switched turn-on wire so that it turns on and off with the truck. if just the yellow has power then it might seem like the radio is on because certain functions can still work without the radio actually being on. like IAAI said, you need some sort of volt meter to test the wires because without one you are shooting in the dark.