I have crossfired RX 480s, both monitors are using an HDMI cable. The first time I plugged them in (a few days ago?) the dual monitor setup worked immediately - no issues. I then updated my graphics drivers and bam, the 2nd card (Linked, not primary) will not detect a monitor plugged in with my HDMI cable.
a few points worth mentioning:
I'm using Windows 7, fully updated (including optional updates.) I've also updated the drivers on both monitors. Please help! First time using a multimonitor setup, and it lasted one hour
You'll need to disable AMD CrossFire if you want both displays connected to a GPU. When AMD CrossFire is enabled, the ports on the second GPU are disabled. Alternatively you could buy a Accell DP - HDMI adapter and connect both displays to the primary GPU.