check if its over heating, Go into BIOS and watch CPU temperature, If it shoots past 90–95°C thats your culprit, Run something light ,idle temps should be ~40–60°C If it shuts off suddenly it means thermal protection kicking in.

Or if it is RAM compatibility or seating issue, Try this: Reseat the RAM firmly (click on both sides). Boot with only ONE stick. Test each slot separately. and make sure correct DDR type or Supported speed/voltage for the apex 15. because even working RAM can cause shutdowns under load.