One DVI port fried or switched off somehow - Nvidia GTX 570

[Robomcd]

I have a now 3-year old GTX 570 in dual monitor setup (was like this from the beginning. Two days ago, the "top" DVI channel seemed to stop working. With top I mean the DVI port next to the HDMI port. I might have inadvertently hit the wrong function button. Whatever, the number 1 display goes shortly to "no signal" and then goes black when switching the monitor or the entire PC on and off.

Already checked
1) I switched cables from port to port and from display to display. Both cables and both monitors are OK.

2) I saw an Nvidia Geforce Experience update coming by that day (December 20, 2015). I uninstalled Geforce experience in the hope that would work, but no dice.

3) Device manager can see both monitors.

4) Nvidia control panel shows both monitors.

5) Screen resolution window shows both monitors, when I extend desktop, one monitor can function either like secondary or as main but the second monitor remains black.

For me this means that at least part of the GPU does see two monitors as viable parts of the system, but just cannot get the signal to the second monitor. Is it possible that the GPU is for whatever reason giving the signal to the HDMI port and that way blocking the DVI port? If so, can I switch that back?

Any other ideas what can be wrong or how to test it?

Again, cables and monitors are NOT the problem.

 

[Robomcd]

Update

I just disabled and uninstalled the card in Device Manager and uninstalled all NVIDIA drivers, did a registry cleaning. Then I also physically removed the card, cleaned and blew the dust out, and reinstalled the card.

Actually, what I did was just put the card back and switched on the PC. Windows 7 (64 bit) did the rest. It works again how it should, both monitors are active and I can switch and extend desktops. I checked the driver with the auto driver-GPU detect website from NVIDIA. I do have an older driver (earlier this year). I will wait a few days to see if it keeps and then update the driver and see what happens.

I don't know what did the trick since I did several things at once without checking each step. Regardless, for the moment, fingers crossed, it really seemed a glitch.

 

[Robomcd]

Next update: problem is back.

OK, I started to play a video on VLC player and immediately black screen. Monitor switching off and on shows something is there but the monitor where the video is playing shows start screen than goes black. stays black. This time the monitor is connected to the other DVI port, so maybe the VLC player is the problem. Any ideas here?