If you only get sound out of one speaker, even when you change input sides, left for right, then it isnt something upstream from your receiver. It is either in your receiver or after it. if you switch speakers, left for right, do you then get sound out of the replaced speaker, but still not the other. then the problem is not the speaker. If you switch speaker wires left for right, and still only get sound out of the same side, then it is not the wires and all that is left is the receiver itself. its just a matter of going through each piece and excluding what works from what doesnt.
I just went through trying to set up a turntable, and went through 3 different phono cables, 2 were bad on one channel, and the other bad on both. I would have gone crazy trying other things, cartridge leads, preamp input, speaker connections etc. if I didnt have a 4th cable to try. So, check the obvious first.