There are 4 diagnostic lights on the Dell 990 CPU numbered 1, 2, 3, and 4. In addition the power button can be blank, orange, or blue. Each combination corresponds to a particular error which can be seen in the below chart.
Light Pattern
Problem Description
Suggested Resolution
The computer is off or not receiving power
Plug the computer into a working electrical outlet and press the power button
A possible system board failure has occurred.
Unplug the CPU for 1 minute then reconnect and power on.
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.
Memory modules are detected, but a memory power failure has occurred.
If two or more memory modules are installed, remove the modules, then re-install one module and re-start the computer. If the computer starts normally, continue to install additional memory modules (one at a time) until you have identified a faulty module or reinstalled all modules without error.
If only one memory module is installed, try moving it to a different DIMM connector and re-start the computer.
BIOS may be corrupt or missing.
A possible system board failure has occurred.
Remove all peripheral cards from the PCI and PCI-E slots and re-start the computer. If the computer boots, add the peripheral cards back one by one until you find the bad one..
Power connector not installed properly.
Re-seat the 2x2 power connector from the power supply unit.
Possible peripheral card or system board failure has occurred.
Remove all peripheral cards from the PCI and PCI-E slots and re-start the computer. If the computer boots, add the peripheral cards back one by one until you find the bad one.
A possible system board failure has occurred
Disconnect all internal and external peripherals, and re-start the computer. If the computer boots, add the peripheral cards back one by one until you find the bad one.
A possible coin cell battery failure has occurred.
Remove the coin cell battery for one minute, reinstall the battery, and restart.
A possible processor failure has occurred.
Re-seat the processor.
Memory modules are detected, but a memory failure has occurred.
If two or more memory modules are installed, remove the modules, then re-install one module and re-start the computer. If the computer starts normally, continue to install additional memory modules (one at a time) until you have identified a faulty module or reinstalled all modules without error.
A possible hard drive failure has occurred.
Re-seat all power and data cables.
A possible USB failure has occurred.
Re-install all USB devices and check all cable connections.
No memory modules are detected.
If two or more memory modules are installed, remove the modules, then reinstall one module and restart the computer. If the computer starts normally, continue to install additional memory modules (one at a time) until you have identified a faulty module or reinstalled all modules without error.
Memory modules are detected, but a memory configuration or compatibility error has occurred.
Ensure that no special requirements for memory module/connector placement exist.
Ensure that the memory you are using is supported by your computer.
A possible expansion card failure has occurred.
Determine if a conflict exists by removing an expansion card (not a graphics card) and restarting the computer.
If the problem persists, reinstall the card you removed, then remove a different card and restart the computer.
Repeat this process for each expansion card installed. If the computer starts normally, troubleshoot the last card removed from the computer for resource conflicts.
A possible system board resource and/or hardware failure has occurred.
Clear CMOS
Disconnect all internal and external peripherals, and restart the computer. If the computer boots, add the peripheral cards back one by one until you find the bad one.
Some other failure has occurred.
Ensure that the display/monitor is plugged into a discrete graphic card.
Ensure that all hard drives and optical drive cables are properly connected to the system board.
If there is an error message on the screen identifying a problem with a device ( hard drive), check the device to make sure it is functioning properly.
If the operating system is attempting to boot from a device (optical drive), check system setup to ensure the boot sequence is correct for the devices installed on your computer.
