Audio Systems: cd player, sony sound, ford focus

Question
i have a 2000 ford focus se. i got a alpine deck put into my car about 4 months ago, it has worked fine until about a week ago. the head unit powers up and looks like everything is working, but it will not play music. when i turn the car on the deck wont turn on until i press a button on it, i never used to have to do this. when it turns on the speakers make a pop nois but thats all i can get out of them. if you have any advice i would really appreciate it. thank you.  

Answer
I'd try reseting the unit first.  you can disconnect a terminal off the car battery and leave it off for about 2 hours, put it back on and see if that helps.  if not I'd remove the cd player and hook it directly to power and a speaker to see if the unit has a problem itself or if there is somthing in the car causing it.  
Do you have any amplifiers in the car?  the focus was available with a sony sound system,  not sure if there is a factory amplifier in the car.  most "premium" factory stereos like bose and infinity, etc. come with a factory amplifier.  they're usually just a black box hidden in the car somewhere so you may not even know its there.  this could've failed.
Try the rest first and let me know.