RX470 unable to see more than one monitor at a time.

New RX470 in old PC (previous HD7950). Three monitors. Two HDMI, one through the DVI.

All show Bios on boot, but as soon as windows 7 comes on, it switches to one display.

Windows only shows one Monitor connected, nothing I can see to change in the Radeon stuff.

If I disconnect one HDMI, the other comes alive on reboot.

I've tried multiple reinstalls of the GPU drivers and downloaded all windows 7 updates.

I'm not even sure if this is a windows or GPU issue. I've been at this for three weeks and I'm still no further on. I might have to return the RX470 go back to the HD7950, but I'd rather obviously solve this.

Absolutely any help appreciated. Thanks.