If all that your Device Manager shows is something like "Microsoft High Definition Audio Device", that indicates that you are using a default/generic driver, which may not be suitable for your hardware. If you are just using the integrated audio device on your motherboard, then just provide the brand and model number of your motherboard and we can look up what audio device it has onboard.
How do I do that without opening my system up? My PC is one of those all-in-one monitor things (like an iMac, but doesn't quite suck). It's kinda like a glorified laptop.