Dell OptiPlex 990 (Early 2011) - Manual (Page 66)

• Ensure that the main power cable and front panel
cable are securely connected to the system board.
LED
Power Button
Problem Description A possible system board failure has occurred.
Troubleshooting Steps Unplug the computer. Allow one minute for the power
to drain. Plug the computer into a working electrical
outlet and press the power button.
LED
Power Button
Problem
Description
A possible system board, power supply, or peripheral
failure has occurred.
Troubleshooting
Steps
• 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.
• If the LED still does not illuminate, the problem is with
the power supply.
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