Stuck at start-up screen after dock replacement

Problem:

I replaced the dock connector of my iPhone 5S, as it did not charge unless I put a lot of pressure on the cable. During start-up, the Apple logo appears, disappears after a few seconds and the screen turns black. The phone is switched on as I can see the LCD is lit. I can switch it off by holding the power button for a few seconds.

What I did:

After replacement, I charged the phone and the Apple logo would immediately appear with some strange squares/lines. I figured something was wrong, reconnected everything and then it seemed to charge fine (battery logo while charging, battery logo with cable when plug was disconnected). After a few minutes, the problem stated above occurred and hasn't changed after charging for a while.

What I've tried:

• Holding the power and home button to reset the phone does not work
• Holding the power and home button while connected to a computer to force reboot mode, iTunes logo does not appear
• While connected to a computer, computer does not recognize device or see that anything is connected.