Hi Aca,
I wouldn't think the speakers are blown. Have a look in the icons displayed beside the clock - theres usually one there for controlling the sound (alternatively you'll find it in the control panel). Note it's not the standard Windows one, it'll be the one supplied by the manufacturer of the sound card. Somewhere in there is usually a setting for a "graph" or "equaliser" and should have options like hall, auditorium, live etc - I'll hazard a guess one of these is on and causing your echo....