Go to mycomputer>windows(C:)>program files(X86)>steam>steamapps>common>tropico3>config

(I suggest you open it with notepad)

remove everything and then copy and paste this:

fullscreen = 0

Save the file, then proceed to open the game it will be completely black but don't worry press esc and the menu should open up, go in settings and set it to your resolution.

Uninstall the game and re install it, its default resolution should be what you set it to.