How can I login my iMac without keyboard (disconnected) and encrypted?

I want to login my iMac, but it is encrypted and ask me password. My wireless keyboard is disconnected because, by mystake, I did disconnected it and turn off the computer, now I can't log in again. How can I login to my user without the keyboard or how can I reconnect the keyboard?

I did reboot the iMac to start the recovery operating system. A window with a keyboard appears and says that I need to wait for my computer to connect with the keyboard. I take off the batteries and put them back, the keyboards starts to blink, a passcode appears, I do type the passcode and click enter, but nothing happens, just says that this computer has connected to this keyboard, the keyboard stops blinking but still not working.

PLEASE HELP!!! (sorry about my english, I'm spanish speaker in Mexico)

I use OS X Lion, but not sure if it is 10.7.4