Why is my laptop automatic turn off?

Hi @rajkumarpandey

Overheating in a laptop is usually due to dust build up in the fan and that the thermal paste on the CPU is old and dried out, preventing good heat transference from the CPU to be extracted by the fan.

Here's the ifixit Toshiba Satellite L300-04P (PSLB8C-04P01X) CPU Thermal Paste Replacement guide that will help.

In Step.26 of the guide, there's a link that explains how to apply new thermal paste to the CPU.

It could also be due to a faulty fan. When the laptop is turned on, can you feel the hot air coming out of the exhaust vent in the laptop and hear the fan operating?