Once more I crave your expertise.
I have recently upgraded to Windows 10 (I'm a devil for punishment)--however, when trying to play some games (at the moment, "Colour of murder") - the resolution is all over the place and makes the game unplayable.-- despite all the usual instructions and Internet advice, no way can the resolution be changed , the alternatives being greyed out.--- any advice please??? ----regards -- Peter.

Do you mean the resolution options are grayed out in the game or on your desktop? Have you tried changing resolution from the desktop?

Hi Draclvr. tks for your reply.---I think the trouble is with Windows 10 --- it is not possible to change the resolution which seems to be the trouble---when I go to "advanced display settings" the resolution menu is grayed out and impossible to change - it stays on 1366x768. give me back windows 7--regards - Peter

Have you tried updating your graphics driver. There have been problems with some Nvidia cards apparently

Windows 10 will automatically "update" your graphics drivers, whether you want it to or not, unless you configure it not to. There is a workaround so you don't end up suddenly having half your games not work because of a surreptitious update, but the default is to download and install whatever is the new driver.

http://winsupersite.com/windows-10/stop-automatic-driver-updates-windows-10

GOG actually has this warning on their webpages for the games they sell:

There is a huge uproar about the forced graphics drivers updates. I have already configured mine some time ago to not do automatic hardware driver updates.

If you did an upgrade, you can revert back to Windows 7 if you do it within 30 days.

There is so much that is good about Windows 10 - why do they have to spoil it with stuff like this...

Wow - somebody really dropped the ball with that decision. That's terrifying. I'm very glad to know about that now and that there is a way to turn automatic driver updates off.

Wow indeed --- thanks to all of you -- it never fails to amaze me of the always ready and helpful support I get from the team , whatever the problem.
And of course , you are right ---I manually updated my driver and - hey presto--the game now works like a dream.
Thanks and thanks again.----
Petjo (Peter)

Glad you got your game to work. I installed Windows 10 straight away in July and within a few weeks I had lots of errors appearing with constant screen freezes. Went back to Windows 7 and reinstalled 10 which works fabulously. So thanks to advice here have now disabled updates for drivers. Will do them manually.

Good for you -- now we are both happy -- regards --Peter