Common Dell Diagnostic Lights
Below are some of the common Dell diagnostic lights and their codes. You should refer to the Dell support site to find your specific model and their codes.
A B C D — No lights indicates the system is getting no power. You can confirm the outlet is working, but if you are still not getting power, you could have a problem with either the power supply, front switch or the motherboard itself.
A — If only the yellow light is lit, this means the computer is off and receiving power.
A B C – If A B and C are yellow and D Green, this means the BIOS is not running or not finishing (completing its POST).
B — If B is yellow and A C D Green, this means you are having some type of issue with the power supply.
C — If C is yellow and A B D Green this means you have some type of problem with the motherboard.
A B D Yellow and C Green –This means you could have a problem with your CPU.
A B Yellow and C D Green — This means you have memory installed, but there is a problem with it.