MC3 is old. First question... is W7 the 32 or 64 bit version? MC3 is 32 bit. If W7 is 64 on the machine, you may get success by running it in the 32 bit emulation mode.
Next: What driver mode and sound card are you using on the computer?
We need to know as much about the computer, it's sound card, the drivers you are using..... if the music is audio based or midi and synths, in order to give you an answer to the question, or more properly, to help point you in the right direction.