Okay. You need to go to the Windows Sound control panel and select the Playback tab. Highlight your output device (if you have no external card there may well only be the one) and select Properties. Then click the Advanced tab and there'll be a drop down menu for bit depth and sample rate. I'd suggest 16 bit/44100Hz (CD Quality) for pure audio that will end up on CD or MP3 or 16 bit/48000Hz if it's going to end up on video.
Next, go back to the Windows Sound control panel, click the Recording tab, and follow the same procedure (highlight, Properties, Advanced) and select the same settings in the drop down menu there,
This should sort you out. In the longer term, consider an external USB audio interface--it'll be hugely better quality and, if it has ASIO drivers, it'll stop Windows applications from changing audio settings without telling you.