help wirh laptop shutting down randomly

[Henroyp]

need help please, Have a pentium Samsung r730 this is the 3rd motherboard testing and the 2nd CPU that ive tested have already tried diff ram, charger and , charger with no battery not sure whats causing it to shut down like this. the fan runs good and also i can get it to work 15-20 min sometimes then it stops working again and keeps shutting down usually after post. all 3 mobos and both cpus do the same so i dont think its that

 

[Unolocogringo]

Have you blown air into the back of the fan outlet to dislodge the layer of dust that blocks the heatsink/fan assembly?