HP ProDesk 405 G2 Microtower Maintenance And Service Manual page 84

Computer powered off automatically and the Power LED flashes Red two times, once every second, followed by a two second
pause, and the computer beeps two times. (Beeps stop after fifth iteration but LEDs continue flashing).
Cause
Processor thermal protection activated:
A fan may be blocked or not turning.
OR
The heat sink is not properly attached to the processor.
System does not power on and the LEDs on the front of the computer are not flashing.
Cause
System unable to power on.
76 Chapter 7 Troubleshooting without diagnostics
Solution
1. Ensure that the computer air vents are not blocked and the
processor cooling fan is running.
2. Open the access panel, press the power button, and see if
the processor fan (or other system fan) spins. If the fan does
not spin, make sure the fan cable is plugged onto the
system board header.
3. If fan a plugged in and not spinning, replace it.
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.