First up: The Receiver has no permanent storage. It has no way of remembering stuff between hard power cycles (i.e. removing the cable).

Is there a way to turn it off?

Not at the Receiver end, no. Turn it off on the PC.

signalling that original PC?

The "original PC" is the one from which it loaded its software (via NFS). If you use an NFS server on the Linux box, it'll attempt to wake the Linux box.