HP EliteDesk 800 G3 Maintenance And Service Manual page 82

System does not power on and the LEDs on the front of the computer are not flashing.
Cause
System unable to power on.
74 Chapter 6 Troubleshooting without diagnostics
Solution
Press and hold the power button for less than 4 seconds. If the
hard drive LED turns white, then:
1. If equipped with a voltage selector, check that the voltage
selector (located on the rear of the power supply) is set to
the appropriate voltage. Proper voltage setting depends on
your region.
2. Remove the expansion cards one at a time until the 5V_aux
light on the system board turns on.
3. Replace the system board.
OR
Press and hold the power button for less than 4 seconds. If the
hard drive LED does not turn on white then:
1. Check that the unit is plugged into a working AC outlet.
2. Open the access panel and check that the power button
cable is properly connected to the system board.
3. Check that the power supply cables are properly connected
to the system board.
4. Check to see if the 5V_aux light on the system board is
turned on. If it is turned on, then replace the power button
assembly.
5. If the 5V_aux light on the system board is off, then replace
the power supply.
6. Replace the system board.