problem with fsx

Hey there, if have a small problem with my flight simulator x.

I installed it this morning and it was running fine at the beginning, I did some missions with no problems whatsoever, a couple of hours ago I tried to play it again, it started up well but after loading for a flight I couldn't see anything!
I could hear sounds but my screen was totally black!

I just want to know what is the problem and what can I do about it

Many thanx!