Laptop 2nd Monitor stopped working

[SalmiSoft]

The 2nd monitor on my Windows 7 laptop stopped working today. It just showed black when I started the laptop. It has previously been working fine and I have not recently made any hardware or software changes. So far I have tried:
- Checking video & power cables are connected correctly
- Removed the video cable & re-connect.
Both monitor and laptop detect the cable removal & replacement but monitor still black.
- Windows-Shift-Left Arrow and Windows-Shift-Right Arrow seem to move the active window between screens.
Still can't see anything on the 2nd monitor though.
- Reboot. No change.
- Connected the monitor to another computer (it works)
- Connect a known working monitor to the laptop (same problem)
- Right-click desktop, select "Screen Resolution" & re-configure the monitors
The 2nd monitor had disappeared from these settings.
Clicked Detect and it was found OK.
Config now looks correct but monitor still not working.

I am running out of ideas. I don't even know if this is a hardware or software issue,
I could re-install the video drivers I suppose, but everything worked OK before so I doubt that is the problem.
So what should I try next?

Okay, SalmiSoft, I'm going to come clean. Everything I know about hardware could fit into a thimble and still have room left over. However, this problem sounded so familiar to me that I had to at least try to help you.

One night, I started up my laptop, and to my horror, the screen was black. The fan was running, the "on" switch was lit - everything suggested that the computer was working. Except for the display. I clacked away at the keys, did an emergency shutdown (twice!) to reboot it, and nothing I tried brought the screen back to life.

Then as I was just about to give up, I unplugged the power cord in defeat, and something shocking happened - my screen came up with my desktop shining brightly. I was saved. But a little confused. I plugged my power cord back in and the screen went black again. It was then that the obvious solution finally flickered on in my mind like a little light bulb.

I looked at the two small brightness keys above the number keys and tapped the one with the up-arrow next to the sun icon. As I anticipated, my screen came back to life. I don't like extremely bright monitors, so I always turn mine way down because it's easier on my eyes. At some point, the brightness key with the down-arrow got clicked without my knowledge and it turned off my display completely.

That was about six minutes of stress I could have done without, but it turned out to have a happy ending for me so I can't complain too much. Hopefully, your problem is just as easily resolved. Good luck.

[SalmiSoft]

Thanks for the suggestion. I never use those keys so it would not have occured to me to check them. I have now checked them all and unfortunately have seen no improvement. The odd thing though is that some of those function appear not to work at all. There is one that looked promising: according to the manual FN + F5 should change the active display device, but I can't see that it has any affect.

I was really hoping my suggestion would nail it, but I'm sure you'll narrow down the possibilities and find the problem eventually. Good luck.