Have you tried with UAC off?
If on Windows 7 have you installed the ALchemy drivers also? They are needed if you are running sound to emulate surround sound on creative cards.
Also try uninstalling the drivers and letting Windows install the default Microsoft ones, as a last resort.
Difficult to diagnose due to the fact it could be a lot of factors causing this, even programs that knock out the focus on game windows so sound disappears.
Ah, sorry forgot this thread.
I had the green cord from my 5.1 speakers plugged into the very greenish grey slot in my soundcard. That was causing all problems, now I get sound in all my games, and Mass Effect doesn't take all sound from my computer anymore.
Thanks.