Speakers/headset:
Web camera:
If your camera is external is it plugged in securely?
In Chrome, is your browser using the correct camera? Click camera icon in Call Screen's address bar, check access and selected camera.
Is other software using the camera? For example Skype is also running. Your computer may require computer reboot.
Do your Firewall settings allow video stream? Ask whoever looks after your firewall for help.
Microphone:
If your microphone is external is it plugged in securely?
Is your microphone being used by the computer? Check computer's audio settings.
Is Chrome using the correct microphone? Click camera icon in Call Screen's address bar; check access and selected microphone.
Are you muted? Either Call Screen, or device's audio.
Is the software using the microphone? For example is Skype also running? Your computer may require computer reboot.
Latest Google Chrome?
Latest Safari?