Where on the PC is it blinking? Please provide a clear picture of where its blinking, if you can. [br]
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Is it blinking in any kind of pattern? If so, it's likely indicating an issue with the diagnostic LEDs, which can be translated here under "***Diagnostic LEDs for the OptiPlex series (2005 to 2009)***":[br]
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https://www.dell.com/support/kbdoc/en-us/000126021/a-reference-guide-to-the-dell-optiplex-diagnostic-indicators[br]
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Good luck![br]