In order to help you, we need to know a lot of information. Make sure to include answers to at least the following questions in your initial post.
- what OS (Windows Xp/Vista, Mac etc.) are you running?
- what FlightGear version do you use?
- what graphics card do you have?
- does the problem occur with any aircraft, at any airport?
- where did you download your aircraft/scenery from?
- is there any output printed to the console (black window)?
- copy&paste your commandline
(tick the "Show commandline box on the last page of FGRun or the "Others" section on the Mac launcher).
If you experience FlightGear crashes, please report a bug using the issue tracker
(can be also used for feature requests).
To run FlightGear on old computers with bad OpenGL support, please take a look at this wiki article
Note: If you did not get a reponse, even after 7 days, you may want to check out the FlightGear mailing lists
to ask your question there.