^First post said it wasn't overheating, but eh.
Normally if the computer overheated and the failsafe killed it... it shouldn't power back on after until it cooled down. Typically.
I said the CPU is overheating, not the computer. Totally different scenarios and symptoms.
In those cases the machine can start up (usually NOT make it anywhere close to booting Windows, often not even BIOS,) then can instantly power-down/restart, quickly overheat the chip again and shut down again... and again, and again, and....
I've actually seen a computer where someone let it keep trying over and over and over again and literally melted the solder of the chip's pins! (Which is a WAY bigger problem at that point!
) The inside of the case never even got warm.
Ditto on the Speedfan recommendation, but be forewarned that - due to the huge variation in board manufacturers/models - it may not display correct values for some of the items it displays.