Found this on the Steam forums:
Problem solved
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I tried to launch the game directly by going to
steam\steamapps\common\the secret of monkey island special edition
and clicking mise.exe.
That didn't work, but I got an error messages "X3Daudio1_6.dll missing".
A quick search in google turned out that this file belongs to directx.
I tried to launch the directx update contained in the directory with the same name and at the end of the install I got a error.
Looking at the logs files (c:\windows\directx.log and c:\windows\DXError.log it turned out one file was corrupt.
So the problems seems to come from a corrupt directx update.
I went to
www.microsoft.com searched "directx" and downloaded the webupdate.
The webupdate downloaded a small 5 mg file.
After that update, install
Framework 3.5 SP1
I hope this may help someone with the same problem.