No output from Bose Lifestyle 12 system
Sounds like you have a problem in the circuits, which of course would take an experience technician to find and repair. But a 1994 electronic item has pretty much reached the end of its expected life cycle (sadly, compared to older equipment which is still working great). Basically, it sounds like the power amp circuit is shutting down a few seconds after startup. Might check to make sure no speakers or cables have shorts, which could activate a protection shutdown circuit. If any of the cubes don't hiss when you turn it on, that would be the first place to look for a problem.