it could be the audio output from the PC man! try goin into the control panel on the pc, in there u will find Sounds and Audio Devices, open that, you'll see and advanced option, click that and at the bottom of the window u'll see the speaker setup option, change output setting about to see if that helps man. theres a whole bunch of options like desk top speakers, monitor speakers etc etc, try them all. if not, it may be the output selector on the amp needs played with. probably wont, but its worth a shot. Phil.