Diagnostic numbers

Hi Hgranillo1977

Thanks for writing to us. 

Diagnostic light 3 and 4 indicate faulty memory or memory slot/s. 

Do let  us know your system model. 

Meanwhile you can try remove all memory modules and add the memory modules back one at a time until the fault re-occurs, test that module in another slot alternatively. 

If possible you can try another memory from another machine . 

Let us know how it goes. 

Regards

Hello,
We are awaiting your response still.
Regard

I have a optiplex 755

Hello nice to hear from you.
Do let us know if you tried the steps as suggested earlier, it will give us a clear picture if its a faulty memory or the motherboard.

Hello
We are awaiting your response.
Regards

What are the memory modules, what do they look like and where do I find them?

Hi nice to hear from you. 

please click on the below link http://downloads.dell.com/manuals/all-products/esuprt_desktop/esuprt_optiplex_desktop/optiplex-755_user%27s%20guide_en-us.pdf

Ensure you select the actual system type in the first page and go to memory removal instructions. 

To make it easy go to page 100 to have an idea on memory removal

Hi,
We are awaiting your response .

Regards