Hi,
I'm running MA3 beta 3 on Windows Vista Ultimate 32 bit.
I'm not sure this is a bug or a local problem but I thought I'd point it out.
After 1 hour of inactivity the monitor turns off, you can't see the aquarium which is expected, but the bubbles and the music still keep playing.
I'm suggesting an option to disable the monitor turning off entirely (I believe I saw this option in MA2), and also make it so that once the monitor is turned off automatically, the sound will also turn off - it makes more sense to me.
Vista (and XP) have a setting in the control panel (power options) to disable the monitor turning off. I presume you're using a desktop rather than a notebook.
I don't think a program like MA3 can reliably determine whether the monitor is off or on - if it can't do that, then it can't turn off the sound automatically when the monitor is off. There could be an option to turn off the bubble and music sound after (some number of) minutes. Probably not worth a lot of effort.