Eliminate the possible and then accept the impossible as the real cause.

First, in Power Options, set the time to shut down the monitor to "NEVER". You might also disable Hibernate, because that too can be a problem source.
Then completely disable Auto Updates. (at least for troubleshooting purposes)

Then to eliminate power line fluctuations from causing intermittent shutdowns, get a UPS (Uninterruptible Power Supply)
Even the smallest UPS, will prevent shutdowns from small power line glitches.
I have six UPS's in my house, because here in Florida, power outages happen almost daily. My UPSs range in size from 300w to 600w.
My 600w UPS backs up my Cable box, TV and a small table lamp, and uses two car batteries for its reserve power. It gives me about 8 hours of run time, during a total power failure. My cable modem, router and Magic Jack device are on a 350w UPS, with a small car battery as its reserve power source. It will stay alive for several hours, during a total blackout.

Good Luck, now get to troubleshooting!