We've designed our studio to work with the simplest of setups: a computer, microphone, and headphones. Since there are thousands of potential microphones and headsets that our users can purchase (not to mention mixers for those of you who record with a host in the same space), it is impossible to provide exact troubleshooting instructions for your gear. After you consider these suggestions, you might want to contact the manufacturer of your device.
Have you connected your device to your computer? (Our how-to is here)
Is your device compatible with your operating system?
Have your drivers or operating system version changed lately?
If you are using analog devices, do you have the appropriate analog-to-digital converters (ADCs)?
If you’ve connected and disconnected devices, have you tried restarting your computer?