DVR RECEIVER Turns Off after 10 Minutes

I have AT&T U-verse & my secondary DVR Receiver won't stay on and keeps turning off after 10 minutes. So far I have had the Modem replaced and the DVR replaced. I also had my house re-wired to accommodate the new Modem. I had an old silver DVR Receiver #IPN330HD so then they switched it to a newer black Receiver # ISB7000.  Secondary TV & Receiver won't stay on.