NX7800GTX-VT2D256E and MSI K8N Neo4/SLI

I have three motherboards, 1 is a MSI K8N SLI-F, the other two are both MSI K8n Neo4/SLI.

I have two NX7800GTX-VT2D256E, running in SLI mode.

When I install the video cards on the Neo4, Windows will not boot up, and at times, the bios wont post. I have reinstalled windows, ran it in safe mode, even tried to boot off of a Ubuntu and Arklinux boot CD to see if i could get at least a GUI to load. Nothing. I tried each video card in single mode, in both slots, and both of them together in each slot in SLI mode. Nothing.

I figure its the motherboard, because two video cards cant be broken. I put them into the other motherboard, same style neo4, same errors. I go out and buy a MSI K8N SLI-F. I put both cards in. Computer boots and installs windows and runs fine.

My K8N SLI-F is now broken, due to god knows what. Wont powercycle on after i moved into my new house. So, I want to use my old K8N Neo4. unfortunatly, i can only use it with my old 6800 GT, since the 7800 GTX dont work.

I have been trying to solve this one for at least a year. No one else seems to have a problem, at least that i know of. You would think a MSI product would be compatible with another MSI product. I am pretty convinced that the NX7800GTX-VT2D256E is incompatible with the K8N Neo4/SLI.

Does anyone have any suggestions?