I ran into this problem in 1.8.2-pre6. I drilled up to bedrock in a 2x2 shaft. Three of the four beacons activated. The fourth would not let me select an ability.
When I went into creative mode and knocked out the bedrock above the broken beacon, there was a piece of netherrack about the bedrock. After I knocked away the concealed netherrack, the beacon immediately lit up.
The offending piece of netherrack was completely concealed by bedrock so there was no way to fix this in survival mode.
Dennis Beach
I ran into this problem in 1.8.2-pre6. I drilled up to bedrock in a 2x2 shaft. Three of the four beacons activated. The fourth would not let me select an ability.
When I went into creative mode and knocked out the bedrock above the broken beacon, there was a piece of netherrack about the bedrock. After I knocked away the concealed netherrack, the beacon immediately lit up.
The offending piece of netherrack was completely concealed by bedrock so there was no way to fix this in survival mode.