Dell OptiPlex 990 Desktop Service Manual page 74

LED
Power Button
Problem Description
Troubleshooting Steps Unplug the computer. Allow one minute for the power to drain.
LED
Power Button
Problem
Description
Troubleshooting
Steps
74
– Ensure that any power strips being used are plugged into
an electrical outlet and are turned on.
– Ensure that the electrical outlet is working by testing it
with another device, such as a lamp.
– Ensure that the main power cable and front panel cable
are securely connected to the system board.
A possible system board failure has occurred.
Plug the computer into a working electrical outlet and press
the power button.
A possible system board, power supply, or peripheral failure has
occurred.
– Power off computer, leaving the computer plugged in.
Press and hold the power supply test button at the rear of
the power supply unit. If the LED next to the switch
illuminates, the problem may be with your system board.
– If the LED next to the switch does not illuminate,
disconnect all internal and external peripherals, and
press and hold the power supply test button. If it
illuminates, there could be a problem with a peripheral.
– If the LED still does not illuminate, remove the PSU
connections from the system board, then press and hold
the power supply button. If it illuminates, there could be a
problem with the system board.