Dell OptiPlex 990 (Early 2011) - Manual (Page 77)

– If the problem persists, the system board is faulty.
LED
Power Button
Problem Description A possible coin cell battery failure has occurred.
Troubleshooting Steps Remove the coin cell battery for one minute, reinstall the
battery, and restart.
LED
Power Button
Problem Description A possible processor failure has occurred.
Troubleshooting Steps Re-seat the processor.
LED
Power Button
Problem Description Memory modules are detected, but a memory failure has
occurred.
Troubleshooting
Steps
– 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.
77