I'm sorry to hear that you're having this issue.
Try moving the cable box to a slightly different location to see if that helps. I'm not sure why the signal from the PN59D550 TV would overpower a cable box's ability to communicate with the remote, but in the past, moving the cable box to a different location may be the answer. If not, the TV may need to be inspected by a technician.
My new Samsung TV (PN59D550) causes my Comcast remote control to stop functioning. If I turn the TV off, the comcast remote works fine. But with the TV on, the remote ceases to work with the Comcast box.