I have tried everything!

I have a NEXUS 7 and it will not power on. I have been reading internet descriptions on what to do. I have tried holding down all combinations of the power and volume buttons, tried with different chargers, I took the back off unplugged the battery for 10 sec and still nothing. NO screen pops up... just black since it shut down, after losing all battery charge. My next step is to call and hope they can repair free of charge though I lost my receipt. Any help? Anything else I can try to do?