you really need to be more specific about what device you are connecting up and how.
listing a model number of what you have as well as photos showing how you connected it would let us know exactly what you did.
from your vague description it almost sounds like you disconnected the speakers from a stereo shelf system and somehow hooked them up to the pc, bypassing the amplifier that power them (which is inside the main stereo shelf system box) which would of course result in barely audible volume levels given pc outputs are not heavily amplified. the proper way to connect would be via any line-in, aux-in or similar input on the main box of such systems.
of course if this is not what you meant... specify.