Phone randomly shut down when plugged into PC, won't boot up

[SourHyperion1]

So, I plugged my phone into my PC. I opened the Windows Phone App for Desktop and the phone asked for me to enter my password. I entered the password and it went to the home screen, then shut down. It sat dark for a second then showed the AT&T Logo, and then went black again. It's been about an hour, and if the battery were dead it should have already shown the battery symbol. I tried powering it on, I tried holding the volume button, etc. Is there any reason why my phone did this and how do I fix it?

 

[Dave Blake]

You held the volume button and power button both down for 20 to 30 seconds?