Sorry to see this is going on with your POD. Unfortunately, it looks like it's too far out of warranty to be replaced if there's a problem with the unit. Paying to fix it may or may not be feasible to you, depending on the risks you're willing to take with used gear. I'd get as basic a setup as possible (POD, guitar cable, guitar only), then using batteries, substituting guitar cables and guitars. If the POD is the only unchanged element of the setup and the hum remains, the POD is the problem.
It looks like your question was answered. If not, post again, as the forums are a good place to find advice about tone, computer configuration, and subjective questions about sound and application. If you have technical questions, you can create a support ticket at http://line6.com/support/...Contact Technical Support, and we will respond to you directly in the ticket.