Hi

After 5 years of usage I believe your notebook is full of dust. Dust blocks air circulation and the notebook cannot be cooled properly. Because of that cooling fan runs constantly and try to cool down hardware components.

In my opinion the first step you should do is cleaning your notebook. If you want to do this properly the notebook must be disassembled. I do not know if you can do this alone without maintenance manual but if it should be done on professional way contact service and let them do this for you.