Both laptop screen and external monitor go black

I have the new Acer Aspire laptop and a TV which I use as a monitor. They have worked together very happily some time now. But yesterday I had to do a forced shutdown when the start button would not work and the TV screen shrank in size and there were error messages. When I rebooted, the TV monitor stayed black and a computer screen came alive for about 10 seconds as it was rebooting, then went black. I disconnected the TV from the computer and started her up and the computer screen behaved itself.
Even if I set all of the display parameters to indicate only one screen (the computer screen), if the TV monitor is connected to the computer, I end up with two black screens.
I have tried many display duplicate and extension.
No new software installed.
There is one clue. I disconnect the TV monitor from the computer, boot up, choose duplicates to display. Then I connect the TV monitor to the computer. What happens, for about one second, is that both screens light up.
What is going on? Help please.

If you are still getting the black screens when starting up there is a useful shortcut you can try. Press the windows key + P. This will give you some options to try different combinations of TV monitor and/or screen.

It sounds like you might need a graphics driver update or roll back to a previous one it is has recently changed.

Hi Philc43. Thanks for replying. I made a wrong assumption and your reply made me question it. I assumed that because both screens were black on startup and remained so, that it would be futile to press any keys as I would be working blind. However, after starting up and waiting until startup had finished, then pressing windows+p, the display menu appeared and I was able to configure. Big thanks.