HP DC7800 - Manual (Page 234)

System does not power on and the LEDs on the front of the computer are not flashing.
Cause Solution
3. Check that both 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
harness.
5. If the 5V_aux light on the system board is off, then replace
the power supply.
6. Replace the system board.
Solving Power Problems
Common causes and solutions for power problems are listed in the following table.
Table D-2 Solving Power Problems
Power supply shuts down intermittently.
Cause Solution
Voltage selector switch on rear of computer chassis (some
models) not switched to correct line voltage (115V or 230V). Select the proper AC voltage using the selector switch.
Power supply will not turn on because of internal power supply
fault. Contact an authorized service provider to replace the power
supply.
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 Solution
Processor thermal protection activated:
A fan may be blocked or not turning.
OR
The heatsink is not properly attached to the processor.
1. Ensure that the computer air vents are not blocked and
the processor cooling fan is running.
2. Open hood, press power button, and see if the processor
fan spins. If the processor fan is not spinning, make sure
the fan's cable is plugged onto the system board header.
3. If fan is plugged in, but is not spinning, then replace the
heatsink/fan assembly.
4. Contact an authorized reseller or service provider.
Table D-1 Solving General Problems (continued)
222 Appendix D Troubleshooting Without Diagnostics