... and the Orbiter.log file shows something likeERROR: DDraw object is still referenced: 50
This orbiter log message is a generic indicator that something went wrong and orbiter tried a shutdown during which it couldn't remove all its previously created graphics objects.
This could be caused by any number of problems, for example by low system memory, by a graphics driver problem, another process running in the background, a misbehaving addon, or by a bug in the Orbiter core.
Try running a fresh orbiter installation (without any addons), use a low-resolution video resolution (say 800x600), try different video devices, turn off all the options in the "Visual parameters" tab, and don't use any high-resolution textures.
If nothing helps, your last option may be posting a message on the forum with as much information about your system (hardware, OS, graphics drivers, DirectX version etc.) as possible. With any luck, somebody with a similar system may have a solution.