I recently was given a Radion HD 5570 from a friend who upgraded his computer. I was running a Radion HD 4650 up untill this point. I installed the card, and left the previous one in so I could run extra monitors in the future. (No. 2 isn't enough. I've been horribly spoiled.)
After an extra long start up, the monitors finally came to life and a check of the AMD catalyst showed that both of my monitors were showing as running from the 4650 even though both monitors were plugged into the 5570. I then tried to install a new version of the catalyst for the 5570. Part way through the process, I black screened and after 15 minutes, I restarted. I'm still getting a black screen. I've tried removing the 4650, starting it with both cards, and starting it with just the 4650.
I'm running a 750 watt PSU so I'm pretty sure the issue isn't with that.
Booting in safe mode by spamming F8? I can't see the monitor for prompts or anything so I THINK that is how to do it. I've been lucky enough to not have to boot in safe mode on this machine in a long while.
I wasn't trying to Crossfire them, more like have a separate card for less intensive stuff on other monitors. Anyways, I'll give it a shot. Thank you for your reply, I'll let you know how it works.