Well, you mentioned that you checked the wires...1) under your hood, near your battery there is supposed to be a fuse. If there is no indicator lights on the amp when the key is turned on then check that fuse first. If there is power past the fuse then you can skip that 2) If that fuse checks out good then make sure that the ground wire is still tightly secured down on both ends(to the car and to the amp) 3) If that too checks out AND with the key turned on all the way without actually starting the car, the head unit does light up as if it is ready/playing, then take a short and small piece of wire and with one end touch the screw/connection on the amp labeled battery positive( could be a plus sign, pos, etc) JUST MAKE SURE IT IS NOT THE GROUND TERMINAL with the other end of your small wire touch it to the smaller wires connector/screw (most commonly a blue wire is used) it will be labeled as the remote turn on lead...if the amp comes on then somehow you lost remote power. There is usually a fuse on the back of your head units wiring harness(on the back of it) If the fuse checks out OK but the amp will only turn on with the jumper wire attached then cut the remote wire behind the deck and tape off the end at the deck. Next, cut the red lead/switched power (only has power when the key is turned on) and reconnect both the previously cut remote wire you didn't tape off and the red wires. The red wires Ned to be reconnected....you are just adding the remote lead to it. If there is a fuse on the amp itself then of course check that first.
