I have the exact same issue(about loading scenarios) and it has been like that for about 2 months, atleast. I have also tried to reinstall the game, didnt help. Have verifed the files in Steam, didnt help. Have tried many different thing, like changing graphics settings inside the game, and outside the game in the controlpanel for my graphics card. Nothing worked.
Have attached three screenshots to show the problem.
Iam running Windows 7 64bit btw.