Cant lower screen resolution for a game

Have spent about 4 hours on this problem and still cant figure it out. Have a Dell XPS 18 all in one, with win 8.1.
I have a online game (Red Alert 1 ) that I have played 100 times over the past year without a problem.
I usually play the game set to a screen resolution of 1024 x 768 and when I start the game it fills the whole screen.
But now it will only let me use 1920 x 1080 if I want it to fill the screen. Any of the other settings will only open a box that is about 50% of my screen. And cant find a way to resize the box.
Tried a number of things including reinstalling my whole pc from a image, reinstalling game with Avast turned off, and a few other things.
Same game works fine on another Dell desktop PC I have and no problem changing the resoultion in the game controls. Whatever I use it fills the screen. Higher res and I see more of the game but items are smaller. Lower I can see the game better. But either way it fills the widescreen monitor like it use to do on this PC.
Appreciate any suggestions.