In some cases reinstalling the redist packages have worked. Look for the resist folder in your AMS install you should see setup files for Directx and VIsual C++. It wont hurt to install these again, if you already have them.
Also look at your "Shared" folder inside the AMS installation, you should have only one file here "coreshaders.mas".
Is it possible you have some mod content that could have broken your AMS?
Steam game files integrity check is a must as well, as pointed out by Stephen... if you delete something as you try to sort out this problem then do additional integrity checks as you go.
And as Marc points out it could be a strange case that sometimes happens where you need to delete your user data files that could be in two places... in My Documents and also the AMS install folder. Look for any config.ini files that you find in the above two locations and delete them as well.
