I did not thave this problem before on my old computer, so not sure if it is a scenery problem not working with my version of windows 7???
Since you didn't had the problem before, and the scenery hasn't changed, it's clearly not a problem of the scenery.
Most likely, is a video drivers problem, judging from your screenshot, the strange triangle is not the only problem you have, textures looks as they are not filtered (see the building roof, for example). This isn't something the scenery controls by itself, but it entirely handled by the video driver.
The scenery does work with Windows 7: a scenery by itself doesn't have any notion of the OS used. The only thing that *might* have had a problem, could be the Addon Manager program the scenery needs to run but, if you had a problem with that, you wouldn't see its menu bar, and you wouldn't see any scenery so, the Addon Manager is surely working on your system. In any case, nothing in the Addon Manager controls image quality or could create something like you are seeing.