maseo

Assuming that you have the Optiplex 780 Mini Tower and not one of the Desktop, Small Form Factor and the Ultra Small Form Factor versions.

Remove the all 8gb of RAM and reinstall only the default memory and see if the system boots.

1x3x Diagnostic lights indicate a memory configuration or compatibility error has occurred.

The Diagnostic Guide and Troubleshooter, is HERE

Bev.

Thank you very much for replying.  There is a two fold problem here. First, I don't have those diagnostic disks, however if possible, I'll be happy to purchase it to them. In fact, i'll be happy to acquire any disk appropriate for this computer. Secondly, ( but most importantly ) the computer does not even get to the logo screen. Once the computer is plugged in, it turns on and immediately begins to beep. One thing I did was to remove all the memory and got the appropriate response meaning that it responded with only the number 1 diagnostic light indicated. I will look into purchasing the diagnostic disk.  thanks, maseo

 maseo

After removing all the RAM, did you reinstall the memory modules that were originally in the Optiplex 780?

You need to contact Dell directly about buy the discs, the forum is user to user, not user to Dell and the members cannot help you purchasing the discs.

All the optiplex Drivers and Downloads, including the Dell Diagnostics for the Optiplex 780, can be downloaded from HERE

Bev.

I just got through browsing through the Dell service site and realized that this computer doesn't have a service tag on it. Is it possible at all for me to purchase any of the system disks? I already purchased a Windows 7 operating system, so i'm talking about the support disk. What do you suggest?

maseo

You can find the system's Service Tag listed in the System Setup [BIOS], Press F2, on startup, to enter System Setup.

See HERE

Bev.

Thank you very much for replying. 

There is a two fold problem here. First, I don't have those diagnostic disks, however if possible, I'll be happy to purchase it to them. In fact, i'll be happy to acquire any disk appropriate for this computer. Secondly, ( but most importantly ) the computer does not even get to the logo screen. Once the computer is plugged in, it turns on and immediately begins to beep. One thing I did was to remove all the memory and got the appropriate response meaning that it responded with only the number 1 diagnostic light indicated.

I will look into purchasing the diagnostic disk. 

thanks,

maseo

I just got through browsing through the Dell service site and realized that this computer doesn't have a service tag on it. Is it possible at all for me to purchase any of the system disks? I already purchased a Windows 7 operating system, so i'm talking about the support disk. What do you suggest?

Well, after some insisting to nagging I got the whole story. This 780 was purchased from ebay as a bare-bones case and mother board. My buddy tried to make it work and couldn't. He took the parts and put them in another computer. Now, I purchased a cpu, memory, hard drive and power supply under the impression that this thing actually worked... at least that's what was conveyed to me. OK, so now I'm invested in this thing and will do what I can to make it work. All the files are being downloaded as I write this from the "Drivers and Download" section of the website.

Staying positive. 

maseo

Hope everything works out for you.

Guess in a situation like this, that's all you can do, is to stay positive and hopefully you end up with a working computer.

Bev.

I had the same problem, you need to boot the system with 2 GB or smaller ddr3 and then update the bios to A05 in order to use the 4GB memory sticks!!