Hello,

I've recently dived into the wondrous world of using a Crossfire setup. However, it's not been a succes so far. I've filled in the template from the sticky:

Graphics Card
XFX HD5870 and Sapphire HD5850, both have 1GB of memory. 
I will try to update this with exact model numbers as soon as I figured them out. 
Both cards are left at stock clocks and voltages. ATI Overdrive is disabled. 

AMD Catalyst Driver Version
Catalyst 13.1, installed earlier this week.

Operating System
Windows 7 Ultimate 64-bit, Service Pack 1.

Issue Details
I often play two games: Blacklight Retribution and Dungeon Defenders.
When crossfire is disabled, both games run at roughly 70 frames per second. When I enable crossfire, both fail to display even the menu. Framerate, as measured by both MSI Afterburner as Fraps, drops to zero. Quitting is only possible trough the use of CTRL+ALT+DEL.
Counter Strike 1.6 seems to be completely unaffected.

Motherboard or System Make & Model
MSI X58 Platinum 

Power Supply
Corsair TX850 (850 Watt output rating)

Display Device(s) and Connection(s) Used
Iiyama ProLite E2407HDS and Dell 1703FP, both connected with DVI cables.

Applications and Games
Any videogame I tried, apart from Counter Strike 1.6.

CPU Details
Intel i7-920


Motherboard BIOS Version
American Megatrends Inc. V1.5 (04/20/2009)

System Memory Type & Amount
Patriot DDR3-1333 CL9, 3x2GB


Additional Details
Windows installation is fresh, did a complete reinstall a few days ago with the two cards and Crossfire bridge in place.
I tried tweaking the many settings in the Catalyst control panel without succes.
Lowering the video settings of the earlier mentioned games has not had any results either.
No error messages are displayed, nor does the rest of the system lose speed. The problem is entirely limited to the game. 

I hope this information is a good start. If more detail is required, I will provide try to provide it. 
I have an intermediate understanding of computers, but I'm entirely new to crossfire.
I hope I can be helped.

Kind regards,
Bert