Cell phone all of a sudden won't turn on

For some reason my cell phone won't turn on. It hasn't gotten wet or been dropped or anything to cause the problem. I was checking a text message, went back to the main screen, hit the top button to turn the screen off, and it seems to have shut to phone off completely. I thought maybe the battery was low and I didn't realize it so I just let it charge until the LED indicator light turned green and it still won't turn on. I took the battery out for a couple of minutes and put it in and nothing. What else is there to do? This is an HTC Evo 3D from Sprint.

1. take out battery
2. hold down the power button for 15sec with battery out.
3. place battery back in phone and put the back on.
4. try to turn on. If it doesn't turn on try a different charger
5. If the above doesn't work maybe take it in to sprint if you have the warranty.

Quote from boltman2007 : 1. take out battery 2. hold down the power button for 15sec with battery out. 3. place battery back in phone and put the back on. 4. try to turn on. If it doesn't turn on try a different charger 5. If the above doesn't work maybe take it in to sprint if you have the warranty.

i tried steps 1-4 already. how closely does Sprint look at who you bought the phone from? I got it used from someone on craigslist but it didn't end up on my account until a couple months ago so do you think they will just see the time it hit my account and assume I have warranty? Do stores even carry the Evo 3D still?

I think they look at the original date of activation. I still have my Evo 3D.

Launch day was June 24th last year, so unless your CL buyer was an idiot (like me) to get it on launch date last year, it is most likely still in warranty.