12-03-2013 10:05 AM - edited 12-03-2013 10:05 AM
Always start with a battery pull. Remove your battery while your phone is powered on (or if there's no sign of life, just remove it) then reinsert it a few seconds later.
If that doesn't do the trick, plug your phone in to your PC and open BlackBerry Desktop Software. Once your phone has been recognized, follow any prompts that appear (one of which might be to reload your OS if a working OS isn't detected by BDS).
Let us know if that helps you.