Member Since: 20th Jun 2015
18th Jul 2017
I wouldn't recommend wiggling a card with power on, however, you might want to try that after shutting the whole system down (if you are handy at opening the computer up - after all, despite them having fans and filters, a lot of dust can build up even in a static PC during the course of a year (or more).
Given both monitors working, but one video output from the computer not working, there's perhaps a problem (as Cheshire has indicated) with a display driver card. You may find "Device Manager" within Settings (search for device manager) under Windows 10. I don't have Windows 8, and would have to fire up a different PC to remember exactly where one finds the same sort of diagnostics (probably under 'My Computer' and 'Properties' in File Manager under Windows XP and 7).
If you look for Monitors or Display Adaptors you might be able to identify what hardware devices are in the computer. Additionally, you might see a message stating "This device is working properly." (or not).
Sometimes it might be a software issue and reinstalling the driver (probably a click or two) may get things back up and running, but if the card is dead (overheated, or whatever) then you might need a local computer shop/ engineer to sort you out. Good luck.