The first thing to check is if your mic is set as your default device as SL uses the windows default as you audio input source. to do that follow this guide:

https://www.tenforums.com/tutorials/111310-change-default-sound-input-device-windows-10-a.html

If the above doesn't work also make sure that "Exclusive mode" is disabled on your mic. Follow this guide to do that:

https://audible.custhelp.com/app/answers/detail/a_id/9463/~/how-do-i-turn-off-exclusive-mode-for-a-windows-audio-playback-device%3F

If the above 2 do not help installing mono can fix this issue. To install mono simply:

1. Right click SCP:SL in Steam and click properties.

2. Navigate to the "Local Files" tab.

3. Click the "Browse Local Files" button

4. Run the file named "mono" or "mono.msi" if you have file extensions turned on. (Do not run monoinstall.vdf)

5. Go through the mono install wizzard and when it's finished restart your PC.

If you still have no voice chat, look at your log from user-faq #15 and you find this: 

* "Important system file that is needed for voice chat is missing, please install all windows updates." You have to install the updates either by using Windows Update tool and installing all updates (preferred), or by installing them manually.

One last thing you can try is to go to the games folder, open the SCPCL_Data folder and delete AudioPluginDissonance then verify the games integrity.

If your voice chat is still broken! We need a bit more information:

* What kind of mic is it?

* Is it wireless or USB?

* Is it set to default?

* Can you hear other people or is it just that they can't hear you? 

* Is it on all servers or only one