Dell OptiPlex 740 Quick Reference Manual page 56

To help you troubleshoot a problem, your computer has four lights labeled
"1," "2," "3," and "4" on the front panel. The lights can be off or green. When
the computer starts normally, the patterns or codes on the lights change as
the boot process completes. If the POST portion of system boot completes
successfully, all four lights display solid green. If the computer malfunctions
during the POST process, the pattern displayed on the LEDs may help
identify where in the process the computer halted.
NOTE:
The orientation of the diagnostic lights may vary depending on the system
type. The diagnostic lights can appear either vertical or horizontal.
Light Pattern
56
Quick Reference Guide
Problem Description
The computer is in a normal off
condition, or a possible pre-
BIOS failure has occurred.
The diagnostic lights are not lit
after the computer successfully
boots to the operating system.
A possible BIOS failure has
occurred; the computer is in
the recovery mode.
A possible processor failure has
occurred.
Suggested Resolution
Plug the computer into a
working electrical outlet and
press the power button.
Run the BIOS Recovery utility,
wait for recovery completion,
and then restart the computer.
Reinstall the processor and
restart the computer.