The HD 6900 series definitely has Blu-ray playback capability.
Can you tell us what has changed between when you could playback Blu-ray and now?
Things i am looking for
1) Monitor connection - HDMI - dvi - vga (any change to wiring)
2) Power DVD software update?
3) Catalyst Driver updates?
4) Are you playing a different disk now compared to before? Have you tried the old disk which worked before?