I have a 10-month-old Dell Inspiron 3521 laptop. It went off and would not come back on. Dell tech came to house and replaced motherboard, power supply, AC adapter and DC input jack. Now, it is shutting off every 30 minutes down to the second, without restarting. Dell diagnostics shows fan is working within their "benchmark" numbers and doesn't feel too hot. Happens whether idle, active, on battery, on AC adapter power, and with or without a cooling pad. Dell is going to reinstall Windows 8 OS, then perhaps new motherboard, then who knows? Not feeling too lucky for success here. Any ideas or suggestions?