Just installed Anthem - PC reboot during online gaming

was playing Anthem tonight (got it for $11 today) and all was going well online with 4 other players and then suddenly my PC did a full reboot. Never had anything like that happen before.

Any ideas why it did that?

Overheating or flaky power supply.

using Afterburner, temps ok. Had CPU OC'ed to 4.5GHz and ok for campaign play but just lowered to 4.4 and all seems ok now