The reason I am focusing on HEAT is:

Most hot CPU's default to shutdown - to prevent serious damage - this is most likely your situation.

A crack in the motherboard may expand when heated and create a gap.

A memory chip (or other) may heat up after a few minutes use.

An accurate digital probe thermometer is a standard diagnostic tool in most tech's workchest.

You have a problem at the moment - but probably not a serious one - have your tech guy check it out. Let it rest for several hours. Try it in the cool of the morning.

Sincerely,
Gargoyle

SIGNING OFF FOR NOW

Heat causes bizarre problems. "Overclockers" have put their machines in small freezers. I use three fans in my most "ancient of days" - with the case cracked open too.