Get the RAM and such from Dell.com so they can support this system.
I have a Dell 6850 that has had 16Gig of ram since birth. Decided to upgrade to 64gig. It is used as a database server.
I bought 64Gig of RAM to replace the memory already in the system. Installed 32Gig on two risers and ordered two more risers. System ran fine for a week on the 32Gig of RAM. Risers came and I installed another 32gig of RAM in the server. The system has stopped cold twice since the second 32Gig was installed.
All memory is identical, matched memory. "C" card was installed first, allowed to sync up, and then the "D" card was inserted - with power off. System came up and recognized 64Gig of RAM - but it won't stay up.