In case of online button we recommend to:
1. Check if agents from department where is the button pointed are available for chat.
2. Use firebug to check if the button is loaded successfully.
3. Check also max queue setting in your button.
In case of offline button we recommend to:
1. Check if "Do not show when unavailable" setting in buttons configuration is not checked.
2. Use firebug to check if the button is loaded successfully.