I am really stuck on this one. I recently got my hands on a second 6870 and I am trying to get it to work with my computer. However as you can guess by the title I get crashes once I get into windows and BIOS reports a hyper transport error. I am no professional when it comes to overclocking and have a very limited understanding of things like busses and northbridges (I am a software dev). I have tried bumping up the voltages of ram and other things in m BIOS but nothing seems to help. The closest I got was bumping my RAM voltage up to 1.59 from 1.5 in which case it lasted about 5 minutes before crashing.
I am completely lost as far as what to do and I have read hundreds of threads and tried various suggestions. I did have another graphics card in there once upon a time which was not as powerful and it ran fine.
I should also note that while I have two 6870s one is made by visiontek and the other is xfx. They are not crossfired (I don't even know how to do this yet). Also I had to get two 6pin splitters because my psu only had two
I'm going with bad PSU. That thing is total junk and should be replaced. Little red voltage select switch, ~575W on the 12V rails (it claims) and only two 6pin PCIe plugs. My 500W PSU had two plugs. If it could really do 575 it should have a lot more, or 6+2 plugs.
125W CPU + 2x150W GPUs + 50W for board and stuff = 475W. I'm guessing your PSU can't even really do that. It could also be a HT error, more so if you are doing any OCing. But that PSU needs to go.