Why did my phone stop turning on and charging completely?

I plugged my phone up a couple of nights ago and when I woke up, it was on the start up screen and all it would do was show me the name of the phone. I tried to wipe my cache but then all it did after I held VOLUME UP + POWER + HOME was stay on a screen that said "Downloading...Do Not Turn Off Target!" After that I pulled the battery, and put it back in ( I did this several times) and tried to turn the phone on and nothing would happen. I tried charging it and it was like the battery was out of it. I even plugged it into my computer and my computer didn't work, either. I have done all I could and still can't get it to work. Please help me as this is a dire situation and it is my only form of communication when I'm away from my house.

Thanks!