My phone shut off and won't start.

Good morning. My phone shut off and won't start. I noticed that it was off yesterday and I thought it was strange seeing it had a full charge. I went to go turn it on and it was dead. I plugged it in, got the little battery with the red line, kept it plugged in and still nothing and almost 24 hours later, still nothing!!! I did a soft reset and it flashes to the AT&T page and then goes right back to the flashing dead battery or black screen. Any suggestions?The phone has not been damaged in any way.

What device are you using? Are you using the original charger that came with the phone?

You may have to flash your phone with the Official OS and Firmware. You will lose data, but can restore your last backup during the set up.
FAQ - How can I recover/reset/restore my phone software? - Microsoft - USA