No sound from from my iMac

When did this issue start? Did you previously get sound from your iMac? What model iMac is it? Did the occurrence of the no sound issue correspond to the installation of any software updates?

I suggest starting with an NVRAM reset:

Reset NVRAM or PRAM on your Mac - Apple Support

Once the NVRAM reset is complete if there is still no sound then verify your System Preferences for sound to make sure that the sound is being directed to the internal speakers and that the volume is set above the minimum.

Change the sound output settings on Mac - Apple Support