Iphone 4 restarts over and over

Hi There

After a drop on the floor, my Iphone 4 IOS 6.1.6, NO physical damage, NO Insurance, NOT hacked and NOT jailbroken, is stuck in this cycle, i keep getting the apple logo and a black screen.

Things noticed while connected to PC
- Phone is not recognices by PC / ITunes
- Restarts over, but only until the Apple logo is shown

Things noticed while connected to wall socket
- Phone starts up
- I can insert pin
- I can work the Iphone for some time (about 1 Minute)
- No carried and no WLAN will be found
- Speaker does not work
- Vibration works
- In the setup, carrier line is not shown and WLAN is grey (can not manipulate)

- Then after a minute it shuts down and restarts

Other things noticed
- Without power, the phone is black
- Can not enter into DFU Mode
- From the inside (completely opened) the phone looks ok and all connectors sit well and the connector cables seem to be good
- After reassembly, same function as stted above

Can anyone help me with this??? Recommend on what to do or what to replace, other than the Phone, haha

Many thanks