Monitor, keyboard and mouse gets no signal

I’ve came to this problem when I tried swapping my older case to a new one. I turned It on, my monitor, mouse and keyboard showed no signal. Before swapping my pc worked fine without any problems. And I’ve tried everything, putting one ram stick In the slot, cleared cmos battery even swapping my parts In to the old case.Just about everything. Am asking if I did something wrong along the way while swapping cases or in the worst case I damaged my parts.
 

misor

Posts: 1,425   +324
Re- check all connections (main 20+4 power, auxillary 4(+4)power, gpu power, connect video cable from monitor to gpu video port)