The blinking green LED on the USB-6008/6009/6501 indicates that the device is connected to a USB port, that it is receiving power from that connection, and that the device is initialized. It does not indicate the device is malfunctioning in some way.
Likewise, if the green LED on the USB-6008/6009/6501/621x is not blinking, it does not necessarily mean the device is malfunctioning; it may mean that the device is simply not initialized. This could be because the device is connected to a computer that does not have NI-DAQmx installed. You can install the latest version of NI-DAQmx by following this link: Download the Latest DAQmx Driver