MiniDisplayPort broken?

For months, I've been using a MiniDisplayPort to HDMI adapter with my MacBook Pro (13" Mid-2012) and an external monitor. It's been a bit fiddly sometimes, but today the connection seems to have given up the ghost entirely. I just can't get video to output to an external source. The monitor and computer seem to both know when the cable's connected, but I just can't get the external monitor to display video.

- It's not the monitor. I plugged my computer into the TV downstairs via the same MDP-to-HDMI adapter, and still got nothing.

- It's not the cable/adapter. I tried connecting my wife's identical MacBook Pro to my external monitor with the same cable, and the external monitor successfully displayed video.

- ... So I think it's the actual hardware port. I've had trouble with the USB ports near the MiniDisplayPort -- sometimes, when they're glitching, the video feed from the MDP-to-HDMI cable would get snowy. The USB ports are working today, though. The MDP apparently isn't.

I've tried resetting the PRAM (no luck), and will try resetting the SMC next. Anything else y'all might suggest, short of taking it in to get it looked at by an Apple tech? Many thanks!