Have you added any new textures or any new aircraft lately.
I hope that you do not download new aircraft or texture straight into FSX? This is really not a good practice to do so.
The only thing that might work would be to restore your computer back to a date where you know it was working correctly. This sometimes will fix problems like these.
It sounds like something has replaced your textures.
WAIT A MINUTE this could also be a video card problem have you updated your drivers lately or are other games giving you problems as well.
This could be a sign that your video card is about to kick the bucket.
The two things I mentioned are the only things I can think of that might create this kind of problem. I hope you figure it out.
