Dell OptiPlex 990 (Early 2011) - Manual (Page 71)

• If the LED still does not illuminate, the problem is with
the power supply.
LED
Power Button
Problem
Description Memory modules are detected, but a memory power 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. If only one memory module is
installed, try moving it to a different DIMM connector
and re-start the computer.
• If available, install verified working memory of the
same type into your computer.
LED
Power Button
Problem Description BIOS may be corrupt or missing.
Troubleshooting Steps The computer hardware is operating normally but the BIOS
may be corrupt or missing.
LED
Power Button
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