Thermal occurrence, the computer keeps shutting down and sending a message of thermal occurrence.

It is very likely that your computer has excessive dust keeping the fans from distributing air for cooling within the unit. It can also be an issue with the power supply fan not working. First, verify the fan is turning properly. If not, replace the power supply. The same thing can be true for the cooling fan for the processor. Check to make sure it is running. To do so will require you to look at it with the side cover off and computer running thus posing a RISK of ELECTRICAL SHOCK. UNLESS YOU ARE CLEARLY VERSED IN HOW TO DO THIS, I ADVISE TAKING IT TO A COMPUTER STORE.

If these two fans are working properly, cleaning the dust inside the computer is the next step.

Disconnect electrical cord from the computer, ground yourself by touching the case to eliminate static electricity, remove side cover from the computer.

Using "canned air" widely available at computer or office supply stores, blow out the dust from the power supply and interior of the computer.