Chosen Solution
I replaced the hard drive in this iMac. No issues. Put cover and glass back on, no video. I take the cover off, and video works fine. I’ve checked to make sure no cables are pinched or disconnected, all fine. I’m stumped. Any help would be appreciated.
Better check again. As you are replacing the cover you are moving one of the video cables (there’s more than one) and losing your signal. You can verify it’s not the logic board/VGC or GPU by connecting an external monitor. If that works normally your GPU/Logic board is ok. You may be shorting the cable as you screw the cover on. Try only using a few screws that are obviously no where near any cables. Also be absolutely certain you are putting the proper length screw in each place - a too long screw may be touching the logic board and either warping or shorting it out. If this answer is acceptable please remember to return and mark it.
