Well, Let's start with sim city. Even though you have the res set to it's lowest. (Probably 640*480). SimCity may be automatically trying to switch it to another setting. This used to happen to me with my old copy of UT. Anyway, the point is, even though it may be not be switching the res, it may be trying to switch the frequency. I.E. You nomally run at 640*480 @ 85hz, but the game is trying to switch it to 640*480 @ 60Hz. If your moniter can't display at the requested Hz, (in our example, 60hz) you get the "Out of scan range" message. Look for a way to change the settings in the game, sometimes you can change a small file in the game folder to have it boot up at another rez. Or hook up another moniter just so you can get the game running, and then set it to default into a range your moniter can run. Shut down and switch back to your moniter. Or, get yourself a nice 23" CinemaHD display.
As for the other situation, I'm unsure.
My Quicksilver DP800 has a GeForce3 card in it. Every so often I will restart, and on reboot the moniter settings will have all changed to a default 800*600, or 640*480. I usually run the highest setting I can at 85Hz, anything lower and my eyes get sore from the flicker. But sometimes the Hz choice disappears, so I'm stuck at 75Hz, unless I drop to 1024*768. Dunno....