my phone turned off and will not turn on again

My phone was on and I put it in my pocket. When I took my phone out 5 minutes later it was off and now it will not turn back on. It had 90% battery when I placed it in my pocket. I have tried holding the sleep button and home button at the same time and I have tried connecting to a charger. Any iddeas on how I can get it to come back on? ?