If there's a global issue with transmitting audio in your voice channel you should first check if you can hear any sounds from your operating system in general. If that seems to not be the case you should first resolve any issues with your audio equipment or settings in your operating system. Googling mostly helps here.
If you're very well able to receive sounds in general you can go ahead and check if Discord is the affected component. In order to resolve that you should verify your Voice & Video settings. Specify the correct input and output devices and also test your microphone inside Discord.
Discord and your operating system are working fine.
If you're able to hear others in your voice channel neither of the two should be the cause of this issue. In that case you can go ahead and check several things.
Does Hydra have the permission to speak? Resolving permission issues can sometimes help fixing the underlying issue. Follow the steps in this article to resolve any permission issue.
Is Hydra muted/server muted? It sometimes happens that either you forgot to unmute Hydra or someone is trying to make a joke out of you. In that case you should definitely be sure that Hydra is not muted in any way.
If Hydra is not muted you should also check if your volume slider is moved down to 0%. If Hydra is quite loud you'd want it somewhere between 3% and 10%, but 0% just resolves into no audio at all.