1/8 plug to rca cable problem

I am trying to run 1/8 from computer with an adapter, it is an adapter that is 1/8 - female rca from Radio Shack. the problem is when I attach it to my Counterpoint SA 2000 preamp I am getting a hum, I am guessing the adapter is using common ground that is causing this. Any suggestions on another cable to use, 1/8 - male rca ???

Have you tried a shorter cable?
Have you tried turning the volume down on the PC?
Have you tried one of the little magnets that clip around the cable to get rid of noise?

Your best bet is to get a USB to RCA adaptor/DAC. There are some on here for under $100
1. I am barely reaching the computer with a 1 meter cable
2. Cable does not have to be plugged in for the humming to occur
3.I don't think that is the problem.
4. Is the USB to RCA linux friendly ???

I found a Monster Cable adapter on ebay, for $10 I am going try that I think.
Does your PC have an optical output?
It does via the usual optional bracket, but I am getting ready to do another computer build ( using a salvaged mobile cpu ) that has and onboard coax/optical.
Problem solved, plugged computer into line conditioner.