iPhone doesn't charge after screenreplacement, is now in boot loop

So I repaired an iphone 4 for a friend. Everything worked, battery life was normal, calling was great, bla bla bla. But after the battery died, he put the phone on the charger, but it just displays a dead battery with like 1% juice in red. If you power it on without charger, it shows the same screen, but with the 30 pin connector.

I ordered a new dock connector from ebay, and I replaced it, but now, when I power the phone on, it only powers on if connected to a wallet or pc. And when I power it on, it shows the apple logo for 3 seconds, goes black, and then again, shows the apple logo for 3 seconds and goes black.

I tried to start up the device without battery but it is still the same.