Well I tried typing alsaconf at the command line, but I received a "command not found" error.
However, I discovered the root of the problem. I guess somewhere, somehow, the option for Headphone mode was altered (I'm assuming Headphone option is only available for laptops?). It was set to line in, which obviously won't put out any sound.
So no wonder I wasn't receiving any error messages!
I appreciate the replies, thank you.