Dell Precision 533CX Setup And Quick Reference Manual page 32

Diagnostic Lights
When you turn on your computer, it performs a series of self-diagnostic
tests. A successful power-on self test (POST) ends with a single beep that
signifies the start of normal operation. If the computer fails to complete the
POST, a series of lights located on the computer can help you understand
which test failed or why the computer stopped responding. These lights
communicate problems encountered before and during POST only, not
during normal operation. To locate the diagnostic lights, see "Computer
Features" on page 10.
The following table lists the codes for the diagnostic lights, gives probable
causes, and suggests corrective actions. The lights are labeled to help you
match the pattern on your computer with one shown in the tables.
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Setup and Quick Reference Guid e