Why does my laptop shut down on its own?

"If it cuts off immediately, it is very likely to be an overheating or power problem.

By ""power-saving activates"" do you mean the fans spin down, etc?
If they fail to spin back up again it's perfectly feasible that the CPU will overheat, even in 10-15 minutes in a cold room.

Consider either opening up and cleaning laptop air intakes, or purchasing a can of compressed air to blow out dust."