[kamocat]

This either means there is a problem with your DB37 cable, or there is a problem with the image on the cRIO, or that the LED is burnt out.
The light should always be flashing or on.
Your orange light (Robot Signal Light) should be plugged into the two pins by this flashing LED on the Digital Sidecar. What is it doing? If it is flashing or solid on, then your little green LED is burnt out.

You can measure resistance with a meter to determine if the cable is at fault. The Robot Signal Light is multiplexed off the serial Relay Output data. You want to check pins 18, 19, 20, and 21.

If the cable turns out good, then try re-imaging your cRIO, and deploy the default code to test.