This happens a lot!

First, verify that your microphone is not muted.  When you enter a Zoom conference call, the default is entering with your microphone muted.  There are a couple of places you can check the status of your microphone: 1)  The bottom-left portion of the Zoom window (which you may have to move your mouse over to see it), and

2)  In the top-right corner of your picture or avatar.  (Again, you may have to move your mouse over that corner to see the Mute / Unmute option.)  Is your microphone muted there?

Do you have a headset with a microphone or a set of earbuds with a mic?  Try them.  Any different results?  Does your headset have a "Mute" button that is set to ON?  If that works, can you use the device that way, or do you need the internal microphone serviced immediately?  If you need the internal mic working, please submit a Support ticket.