unable to boot my MacBook after FileVault 2 activation after activation of FileVault 2 I am unable to boot my computer, the apple sign turns into a prohibitory sign with a spinning circle beneath it , that spins forever. I really need the data on this computer :( and I can not afford the very expensive data recovery services . Does anyone know how I can overcome this problem or at least decrypt and save my data ?
You can press the option + R key to boot into recovery mode. Then using Disk utility and follow this guide to decrypt the partition:

http://derflounder.wordpress.com/2011/11/23/using-the-command-line-to-unlock-or-decrypt-your-filevault-2-encrypted-boot-drive/