|It is not uncommon for components/cables to become slightly dislodged when a system is moved.|
Turn off all power. Open the case. Re-seat all cards & cables. ie take cards such as Graphics card and ram out of their slots and re-insert them ( Several times as that will work to clean the contacts) . Do the same for power & data cables.
If you still get a "Signal Out of Range" or similar error on screen after this then the graphics card might have failed. You did have power disconnected when switching cables????
Goin' Fishin' (Some day)