See the article at the link NJBlackBerry posted above. Also browse the the rest of the faq and get your bearings.
You'll need JL_CMDER, the blackberry desktop software, and the blackberry handheld software (the OS).
Follow the instructions you'll find when you download the software and install whatever you don't already have. Be sure to install the handheld software; don't just download the installer and stop there.
Then, wipe the blackberry using JL_CMDER then use the desktop software to reinstall the OS.
sorry to follow up but have you tried a battery pull? I know it sounds simple and some of the more experienced people many criticize me for saying it but I have seen alot of posts where people never tried it