The most common reason is a wrong server address or port. By default, TeamSpeak uses UDP port 9987 — if your router or firewall blocks UDP traffic, the connection simply won't go through. Check your firewall rules and make sure the port is open. If you're on a corporate or university network, that port is often restricted by policy.
Go to Settings → Options → Playback and Capture. Run the device wizard and make sure the correct input and output devices are selected. Windows sometimes silently switches the default device after an update, and TS doesn't follow that change automatically. Also check that the app isn't muted in the Windows Volume Mixer.
This usually points to a keep-alive issue. Go to Options → Advanced and enable the "Keep alive" packet option. Also check your router — some home routers close idle UDP sessions after 30–60 seconds. If the server admin allows it, ask them to adjust the UDP timeout on the server side.
If your password reset email isn't arriving, check the spam folder — messages from teamspeak.com often end up there. If the email does arrive but the link doesn't work, try opening it in a different browser. Clear the cache first.