Maybe RAM, or CPU issue, as there is no dedicated GPU.
If nothing appears on internal LCD, then DP video output could be damaged from previous repair attempt.
Check diode mode al data lines from LCD connector.
Be sure no moved, or knocked off components there.
Also check all traces continuity.
What makes it a hopeless project? There isn?t any visible board damage whatsoever. Only the internal connector itself was messed up when it arrived. Pads are all good and have continuity with new connector. Could U4500 have anything to do with it??