Hi,
For the USB-6216, if the LED is not lit is for two possible reasons:
1. You have an incompatible DAQmx version installed in your computer. In the next page you can check the minimum required version of driver for each OS.
NI-DAQmx First Available Hardware Support
http://www.ni.com/product-documentation/55084/en/
2. The device could be damaged. If you tried different cables, different computers and all of them have the correct version of the driver, it is possible that the device is broken.
Hope this information was useful for you.
Best regards,
Cesar Ortega
Technical Support Engineering
National Instruments
www.ni.com/support