Start with the right checks.
No lights or display is different from a Mac that shows a startup symbol. Begin with what the machine actually does when you press power.
What to do next.
Check the adapter, cable and wall outlet. Use only an undamaged, compatible power supply.
If the Mac has an external display, check that display’s power and connection too.
If the Mac shows no sign of power, hold its power button for about 10 seconds, then press and release it normally. On a Mac laptop with Touch ID, that is the Touch ID button. Disconnect unnecessary accessories before repeating the check.
Record any sound, light, logo or symbol that appears. Note the model and whether it uses Apple silicon or an Intel processor.
Check the result.
If it starts, save important work and check whether the problem returns with a particular accessory attached.
Stop and get help if…
The Mac remains unresponsive, the power equipment is damaged or a disk makes unusual sounds. Physical repair may be needed; a remote session cannot replace a failed power supply or retrieve information from every damaged drive.