Your options:
A:
1 - Reset the AP
2 - Make one of the working APs the virtual controller and have it adopt all the rest of the APs including this one
B: Enable the LAN port on this one AP
1 - Log into this AP via console port
2 - Run the following commands:
>en
#self
#int ge 1
#show context
If the port is disabled you should see a line stating 'shutdown'
In this case re-enable it
#no shutdown
#com wr
#show context
I hope this helps,
Christoph
Christoph S.