I'd start by looking for an updated audio driver, and see what that does for your problem.

Though in the end the solution may just be you have to get a PCI sound card. It doesn't bypass the motherboard, since the motherboard is like the central nervous system of a computer, but it does bypass the onboard audio.

You may even want to consider just taking the thing back. You've already gotten a taste of what you can expect from HP tech support, and you're only 11 days into owning the thing. I have to say, that answer that it's an ISP issue has to at least be worthy of nomination for the stupidest answer ever given award. It's clearly an issue with your system. Whether it's software or hardware is what is left to determine. But since HP will clearly be no help in the future, and this early on you're having problems, might be time to cut your losses and look for a different brand computer. HP is hardly known for quality, so there's that as well. So long as it's not an Acer brand (Acer, Gateway, eMachines) or HP's other brand Compaq, you'd probably be hard pressed to do worse.