If you were to consider it worth it, MB's for it are fairly cheap on eBay.  But you might make some money selling the parts instead. Another trick is to remove the CPU, turn on and see if throws an error code.  But it should've gave the RAM error code when it was removed.  Also, there is a CPU error code, and it didn't throw that. You're welcome for the help.  Too bad we didn't have better luck.
I recently came into possession of an Optiplex 780 MT from a school. I had wired everything I could, and everything seemed to be fine, turned on the PSU and computer and was met with a Solid Amber power button, along with a Solid green HD service light. I've swapped Hard drives and cables, still no success.    
Dell optiplex 780 MT solid Amber power button along with a green HD service 
light