MB C3 MUX Repair Bad connection between PC/MUX?

[scaro]

Hi

I have an MB C3 Mux im trying to fix. Its for a friend at work. I have fixed other problems with it before but this time i dont know where the problem is.
Problem is that it shows "Unlocked D" but only holds that for some seconds sometimes less or nothing. It then goes to "not connected". It started i while ago and have become worse and worse

Does anyone know what the error could be?

Its the version with blackbox with stuff inside

[scaro]

A short clip showing the problem.

[scaro]

Have forgot to tell what i did. I think i changed to a different usbadapter cable, strange as the one used have worked before