Document the symptoms
Write down what happens, when it started and whether anything changed immediately before the problem. Note error messages, unusual sounds, heat, battery behaviour and whether the fault appears only under load.
Protect data first
If the system still starts and the drive appears healthy, back up important files before troubleshooting. If the drive is clicking, repeatedly disappearing or causing severe read errors, reduce unnecessary use and consider professional recovery advice.
Check warranty and repair economics
Opening some devices can complicate warranty service. Compare the repair estimate against the age, condition and replacement value of the computer. A battery, SSD or fan replacement can be worthwhile; a major board repair on an old low-value laptop may not be.