|In my experience, a soundcard either works properly (as long as the correct sound driver is installed) or it fails and doesn't work at all, so I don't think it's a hardware problem.|
Re-installing the sound driver may correct the problem, or check the driver supplier's website for a newer version.
If it's a factory-built PC using on-board sound adapter, or a laptop, the driver supplier is your PC/laptop maker's website.
if it's a custom-built/home-built PC using on-board sound adapter, the driver supplier is the motherboard maker's website.
If it's an add-on sound card which has been installed in a PCI slot, the driver supplier is the card manufacturer's website.