Odd technical advice for a broken (?) steam game.

I'd tell you to verify the game cache. It might work, not sure though.

Get the exact error message you get and google it. Such a typical advice but honestly it's your best bet. It's likely that someone else had the same problem as you and asked somewhere on the internet. Possibly even got an answer.

I just checked the game myself, and it still works, so the game itself is fine, just in conflict with something on your system, evidently. Not sure if this would work, but wondering if your save broke somehow? Try going to your savegames, which are located in your documents folder, and moving them elsewhere, to see if it works without them, perhaps?

delete windows vista

Might want to try running in compatibility mode for an older version of windows.

Sounds like a broken save after reading all of this. If you can not load a different save or make a new game ( IE same issues with those two ) Then you might have to uninstall and re-install the game. Only thing I can think of at this point. ( Since verifying did not work for you. )

Might be a compatibility mode issue but I really doubt it, MA1 is old but not THAT old. If it was Dungeon Keeper 2 then yea it would be a compatibility issue and you would have to find workarounds ( the modes vista has will not work with DK2 no matter what you try. So you will have to look online for workarounds. )

Man, I hope you hadn't done the bullshit that was Feros first...

Vistaaaaaa

have you changed the hardware? (graphics card / ram etc...)
even though i doubt it for me1, some games error if you have too much ram
i.e Act of War: Direct Action ( i have to go through msconfig and set it so i have 2 gigs max running on boot to play it)

Make a screenshot of the error then post it here.

Mine doesn't work either, reinstalled everything I couldn't even start it up.