Power on the computer
Check for fans spinning and lights turning on
Listen for beep codes
Watch for the manufacturer logo or BIOS screen
Check whether the keyboard responds, such as Caps Lock or Num Lock lights toggling
Check whether the display shows any image or error message
Verify that the system reaches BIOS/UEFI setup
Confirm that storage devices are detected in BIOS/UEFI
Confirm that the system continues past the POST screen and starts booting an operating system
If there is no display, test with another monitor, cable, or graphics output
If there are beep codes or diagnostic LEDs, compare them with the motherboard manual
If the system powers on but shuts off immediately, check the power supply and connections