iPhone 4 will not turn on after use

I recently made used my iPhone4, putti down for 30 minutes, came back & it will not turn on or charge. I had a full charge on it prior and I tried to charge it again and no avail, it will not turn on or respond. I've had it for just over 2 years. Any advise, I am assuming that they can't fix it or exchange & I'll have to buy a new one?