If it is one STB, focus on checking power and connections. If one or more but not all are having a problem, check the cables and wiring – it could be a non-standard or defective Ethernet or HDMI video cable. Borrow or purchase a new Ethernet cable and see if it fixes the problem. If the issue persists, try replacing the HDMI cable, then move on to the other cable types until you isolate the problem. If all STBs are out, start checking at the gateway, then the STB/PVR.