I have a pair of Polk HIPS HB speakers that came with my Dell computer. I have them plugged in, the pc Windows volume is at 95, but the sound coming through the speakers is barely audible. I have to put the speakers up to my ears to hear the sound. The speakers have two small dials under the base (for gain adjustment??)... one is set at 4 and the other at 1. I have tried to turn these up but they won't turn. Suggestions?