Crackling and sound going out with digital optical setup. Can't fiqure out if its the a/v receiver or pc motherboard

[TechnologyHatesMeButILoveIt]

The optical cable is connected to my pc and 7.1 channel home theater. One day I started hearing crackling and the sound would go out for a few seconds, around every minute or so. I replaced another cable, no change, then bought a new $35 cable, still the same results.
It happens with both optical ports on my Yamaha a/v receiver, though the second one is not as bad. And there doesn't have to be sound, its crackling right now as I type this.

I don't want to believe its my motherboard, its brand new, and I am pretty sure this started happening a week after replacing a MSI board with a gigabyte board.

My a/v receiver is a little over three years old, and as the same happened with my first Yamaha receiver, the HDMI ports stopped working. I only have two working HDMI ports out of 4 with this one, so it would not surprise me if other ports like the optical port stopped working.

My question is how can I tell if its the receiver or the motherboard's port? I can't just buy a $350+ receiver to only find out its not the problem.

And if it is the motherboard, how can I have sound through my home theater without a optical cable? The receiver is already connected to my tv, with a blu-ray and satellite receiver connected to the inputs, and the tv is the output. Every time I tried to connect a hdmi to the receiver from my computer, all that happens is my tv suddenly becomes the monitor for my computer...

And I refuse to replace any more computer parts. After three MSI boards, two graphics cards, 1 psu, and four sticks of ram, I will take a few minor sound problems any day before going though that again.

 

[BadBoyGreek]

I had a similar problem years ago with a preamp and it ended up being the optical input board on the preamp. If you're finding that there's a difference in the sound between the two optical ports on the receiver, odds are that's your point of failure.

Instead of buying a new receiver, you could buy something like an inexpensive optical to coax or RCA output adapter and try forcing your computer's sound through other inputs to rule the receiver's optical inputs out.

 

[TechnologyHatesMeButILoveIt]

Is there a way to do it with a normal hdmi? I have a twenty-five foot HDMI, which is just barely long enough. If I can do it that way, it would be better than waiting until Tuesday for amazon to ship a coaxial cable. The closet store I could buy one at is an hour away.