iPhone 4 Won’t Turn On or Wake Up?
Unfortunately, it sounds like your iPhone 4 has had it. If iTunes can't recognize it, then something is seriously wrong. The only thing I can think of is that the battery got disconnected, but that's not likely. The best thing to do is to sell "For Parts or Repair" on easy to pay for part of a used iPhone, but older models can be pretty inexpensive. A used iPhone 4 should cost only about  $75-$100, while a 4S should run $110-$130, a 5 for about $200, and an iPhone 5S for about $350.