OBS Studio doesn't record sound when recording

[JennaIsEpic]

Today, I wanted to post a video on YouTube, but when I recorded a video there was no audio at all. Yesterday, when I recorded a video there was audio and it worked just fine. I had OBS for about 4 months, but I started using it yesterday. I tweaked a few things yesterday, but the audio was fine, no problems. What do I do to capture Desktop Audio and Mic/Aux audio?