You possibly have a failed power supply. From the CLI you can run: show power-supply-status. This will give you output like this:
show power-supply-status
--------------[ Power Supply Status ]---------------
Power Supply 1 : Present
Power Supply 1 : Connected to power source
Power Supply 2 : Not Detected
Power Supply 2 : Not connected to power source
Contact Cisco for a possible RMA of that power supply. I have about 130 sensors in our environment and have had many power supply failures, and all have ended up in RMA.