Who is THEY?
THEY messed up by not testing it!?!
Seriously, cables most likely issue here, check connections on both ends, swap them out for new ones if doesn't help.
Reseat the video card as well, moving could have loosened it in the slot, might as well clean the slot too, if going in there, and the fan, with can of compressed air and soft cloth, while unplugged of course.
A very sloppy move could break the cables, they are delicate creatures especially if the cheapo variety.