Possible reasons could be:

☛ PC being overheated.

☛ Dust having being accumulated all around.

☛ CPU fans not working properly .

☛ Faulty power connections.

☛ Faulty circuit board from where the power is being drawn.

☛ Support Drivers not having being installed.

Debugging steps which can be taken are:

☛ Cleaning the system thoroughly and maintaining it in a dust-free environment. Environment that is cool enough and facilitates for easy passage of air should be ideal enough.

☛ By locating the appropriate support drivers for the system in consideration and having them installed.