I have an Optiplex 780 mini tower with 2 DDR3 2 Gb. I try to replace it with 2 new Kinsgton KHZ1333C9D3B1/4G x2 non-ECC. When I plug the new memory, I have the 3 4 light error.
According this guide http://i.dell.com/sites/content/business/solutions/engineering-docs/en/Documents/optiplex-780-tech-g..., the Ram shoud work.
I upgrade BIOS to A15 update
I ran into this very issue a few months ago. Also with an Opti 780 Tower.
What I did was go to crucial.com and used their memory configurator to identify the exact specs I needed and then found the memory on Newegg that matched the spec.
It did not work.
Went back to crucial and ordered the ram directly from them. It did work.
There are minute differences that obviously matter.
With that said, I have never had a problem with the crucial memory configurator.
I checked the kingston memory configurator after reading your post. They don't even list the 780 in there dell optiplex section.
And stay away from the patriot site. Last time I used their memory finder it popped up both ddr2 and ddr3 for one system. Out of curiosity I just checked their site, they also don't list the Opti 780.
Try installing a single 2GB module, remove any other installed modules. See if it boots okay, else remove the memory and repeat the same process with the second 2GB module. See if the second module boots. If both do not work individually then try getting Dual rank (2R) memory rather than single rank (1R), your kingston memory is a single rank.
The specs are correct. So either the module is defective or maybe it isn't accepting the single rank module.
It all comes back now. Single vs Dual rank. I remember researching it and not being able to come up with a way to tell the difference if it is not specified on the chip.
So. How did you determing that the 780 uses dual rank.
And how do you know what the memory is if it doesn't state 1Rx4 or 2Rx4.
The memory I had my user order (that didn't work) was F3-1333C9D-8GNS. Google that and you get links to both gskill and newegg, but in neither place do they tell you what the rank is.
F3-1333C9D-8GNS is a Dual rank memory acc to this website - http://www.mindfactory.de/product_info.php/8GB-G-Skill-F3-1333C9D-8GNS-DDR3-1333-DIMM-CL9-Dual-Kit_9...
How did I determine 780 uses Dual rank? Most of all the system supports support single and Dual rank memory besides most online retailers recommend dual rank 4GB modules for your system.
Generally Single Rank Memory is faster than Dual Rank Memory, in laymen’s terms when a computer accesses Single Rank Memory it only has to go around the track once, where are Dual Rank it would have to go around the track twice.
If the manufacturer doesn't specify the rank on the label of the memory then you need to google the part number - like F3-1333C9D-8GNS. If the manufacturer doesn't specify it then it's hard to find.
The Kingston module which you mention was a single rank so I thought maybe rank was an issue. If even dual rank memory didn't work then something else might be the cause or maybe both are simply incompatible. Try other brand memory like Samsung, Hynix, Kingston value RAM or crucial.