I built a computer recently with an AMD A6-3670K 2.7GHz Quad-Core Processor APU. I had no previous graphics card and was just using the built in graphics of the APU. My friend gave me his old Asus HD6670 video card since he got a new one. I put it in and installed the recent drivers and he told me that i could crossfire the graphics. I am not sure how to do this though. Currently i am using the video card's hdmi port to my monitor and after a while i will get a black screen and have to shut down my computer. I am assuming this is because i did not crossfire the two correctly. Any help would be appreciated.
This is what my computer was before adding the video card:
AMD A6-3670K 2.7GHz Quad-Core Processor
Gigabyte GA-A55M-DS2 Micro ATX FM1 Motherboard
Corsair XMS3 8GB (2 x 4GB) DDR3-1333 Memory
Western Digital Caviar Blue 500GB 3.5" 7200RPM Internal Hard Drive
Rosewill 500w PSU