My computer is no longer sending signals to any of my external hardware

My computer still starts up making the same sounds and lights and such as usual, but there is no longer any signal to my monitor, mouse, keyboard, or speakers. I discovered this upon trying to wake it from sleep mode, the computer woke up, but no lights turned on on the keyboard, no sound came out of the speakers, and my monitor said no signal.

This happened once before, and we took it to a local repair place. They hooked it up to their monitor and keyboard and it worked fine. I've tested my monitor on another computer and it works just fine, as well as the rest of the hardware. Last time they said something had likely unseated itself, and the ride in the car had reseated it. What should I try?