Go into Taskmanager and see what is using up the CPU.
If nothing running System Idle process should be showing about 96% that is normal.
Let us know what else is using up the CPU.
Have you ran any of your security programs.Maybe download update and run the free version of Malwarebytes to see if that finds any faults.
Is it a while since you gave it a clean out.Check the air vents are not clogged up with dust or fluff if so inside will also need cleaning.