The Cisco 7940G and 7960G are pre-PoE devices. They will not be able to get power from the PoE switch.
The following link is provided for reference and may provide further information regarding the incompatibility betweencompliant devices and Cisco s.
Note: This may include other Cisco IP Phones that are not 802.3af compliant. For further information on your Cisco IP Phone, please contact Cisco.