Orbiter renders stars (except for our sun, of course) as single pixels of varying intensity. This makes them quite faint (in particular at high screen resolutions), but also fairly realistic.
If your Orbiter definitely doesn't show any trace of stars, first check for the obvious: make sure that the star count, brightness and contrast levels under the "Parameters" tab of the Orbiter Launchpad are set correctly. If this doesn't help, and in particular if you also don't see any grid and constellation lines in "Planetarium" mode, then the most likely problem is the anti-aliasing setting of your graphics card. Try to open the configuration tool of your graphics driver, and disable anti-aliasing.