Buzz from the speakers uding PC and Power Amp.

When I hooked up the PC directly to the power Amp. I've got loud buzz from the speaker but not with the cd or tuner.
Thanks in advance
The PC power supply ..
Is the PC connected to the same A/C source?
I would try removing the ground of the PC's A/C cord.
Either some dc current, or a ground issue.
If you cconnected the PC via a toslink to a DAC as part of the stereo, it would also solve the issue.
Wrong. Your speakers want to have nothing to do with the PC. That's the cause.