Asus P5B - Manual (Page 44)

 ASUS TeleSky User Manual
Cable deployment may be incorrect or your PSTN
phone line is not properly connected. Check all
cable connections and run the device set-up
diagnostic utility on the support CD.
The ASUS TeleSky utility may not be running.
Launch both the utility and Skype to ensure a Skype
dial tone is heard.
You may not be logged into Skype. Log in to your
Skype account.
The Skype sound settings may be incorrect.
1. Go to Skype > Tools > Options > Sound
Devices.
Why is there no Skype dial tone when I enable
Skype Dial mode?