Dell OptiPlex 990 (Early 2011) - Manual (Page 78)

– If available, install working memory of the same type
into your computer.
LED
Power Button
Problem Description A possible hard drive failure has occurred.
Troubleshooting Steps Re-seat all power and data cables.
LED
Power Button
Problem Description A possible USB failure has occurred.
Troubleshooting Steps Re-install all USB devices and check all cable connections.
LED
Power Button
Problem Description No memory modules are detected.
Troubleshooting
Steps
– 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.
– If available, install working memory of the same type
into your computer.
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