Check to see if the model number for the stereo is a recalled item. Many electronics were outsourced and then installed into the automobile. Warranty or not, seems as if the stereo has been tampered with. Best to buy a new one.
First, check the battery power for its full potential power. Test, battery. If results from test say battery is:Good, then crank the engine and hold down the gas pedal. If car still does not start, visually inspect the fuses. Focus on the fuel pump areas.