Dell OptiPlex 780 - Manual (Page 14)

3-4-3 Search for video ROM failure
4-2-1 No timer tick
4-2-2 Shutdown failure
4-2-3 Gate A20 failure
4-2-4 Unexpected interrupt in protected mode
4-3-1 Memory failure above address 0FFFFh
4-3-3 Timer-chip counter 2 failure
4-3-4 Time-of-day clock stopped
4-4-1 Serial or parallel port test failure
4-4-2 Failure to decompress code to shadowed memory
4-4-3 Math-coprocessor test failure
4-4-4 Cache test failure
Diagnostic Lights
To help troubleshoot a problem, your computer has four lights labeled 1, 2, 3, and 4 on the bank panel. When the computer
starts normally, the lights flash before turning off. If the computer malfunctions, the sequence of the lights help to identify
the problem.
NOTE: After the computer completes POST, all four lights turn off before booting to the operating system.
Light Pattern Problem Description Suggested Resolution
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.
Plug the computer into a working electrical outlet.
If the problem persists, contact Dell.
A possible processor
failure has occurred.
Reseat the processor (see Processor information for your computer).
If the problem persists, contact Dell.
Memory modules are
detected, but a memory
failure has occurred.
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.
If the problem persists, contact Dell.
A possible graphics
card failure has
occurred.
Reseat any installed graphics cards.
If available, install a working graphics card into your computer.
If the problem persists, contact Dell .
A possible floppy drive
or hard drive failure
has occurred.
Reseat all power and data cables.
A possible USB failure
has occurred.
Reinstall all USB devices and check all cable connections.