Your PC might have Dell diagnostic lights labeled A B C D on the rear that can help you diagnose problems with your Dell machine. Not all models will have these, but if your computer does, you can reference these and quickly repair a problem that might have taken you days to figure out. If your computer does not have lights, it will probably only issue a beep code, which is fine. However, the lights can confirm things a beep code cannot, such as no power to the system.

Dell diagnostic lights

The image above shows a working Dell with all four lights green. If, however, you have anything different, you can look up your model on the Dell website for further documentation on these error codes. We will list a few of the most common here, but there are certainly more on the Dell website.

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 ligth is lit, this means the computer is off and receiving power.

A B C – If A B and C are yellow, this means the BIOS is not running or not finishing (completing its POST).

B — If B is yellow, this means you are having some type of issue with the power supply.

C — If C is yellow, 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.

These are the top Dell diagnostic lights and their conditions that can prevent your system from booting. You may have different diagnostic lights and still be able to boot, but a lot of those problems can be quickly fixed once you boot up the computer. One important thing you can try if you are receiving any of these critical conditions is to shut the system down, remove the plug and open the case. Make sure you touch a piece of metal on the case’s chassis to ground yourself, then proceed to making sure all cables and cards are secure. Be careful not to touch any chips on the memory or the motherboard in the process.