iPhone went off, boot-loop when at the recharger

Hello,

a few days ago my iPhone went off although the battery was loaded.

Few times i managed to turn it on again but now it is off and won't turn on. When i connect it to the recharger it gets stuck in a boot loop. That means: the display is black and off, than it turns on the white apple-logo appears for a few seconds, than it disappears and the display is off, after a few seconds it turns on again but it won't get further than to the white apple.

I tried to reset but it is all the same.

I would be very glad for an advice what the problem could be and how to solve it. Can i replace something to make it work again?

I have no guarantee. Please help.