For starters, what kind of an install are you talking about? Steam, the Amazon direct download, or from an old CD?
If you used an older version for your install, did you also install the 1.04 patch?
Does what you have installed now work? Can you run the game and all of the playable platforms?
What else have you installed? Are you running the LWAMI or RA mods?
What happens if you go into the Mission Editor and load one of the new scenarios? If it loads, look for error messages or try just saving the scenario and see if it works.
Think about what you've done so far.
