iPhone 4S only powers on when plugged into a wall charger, stuck in bootloop
Today I went to get my phone's screen fixed. At first, the problem was that the phone was rebooting every 3-4 minutes. Then, after it died, it doesn't power on anymore, except when it is plugged into a wall charger. However, it is stuck in a bootloop, where it shows the apple logo for about 7 seconds, then the screen goes black for about 5 seconds, then repeats. I can't unplug it or else the phone goes dead, and plugging it into my computer results in the same deadness. I've tried DFU Mode, Recovery and everything else when plugged into my computer, but it remains dead and black screened. The phone is not picked up at all, it doesn't power on or anything. It only powers on when it is wall charged, but it will bootloop. I can't get past this, and there is no way I can restore it. Help?
iPhone 4S, iOS 8.0.2