If you're not concerned with the data then you can wipe it with JL_Cmder and reload the OS.
1. First locate your carrier and the OS file you wish to use. BlackBerry - Desktop & Device Software Download Sites for BlackBerry users - US
3. Download the OS file from step 1 to the PC then install it to the PC by running (double clicking) the file you downloaded.
4. Go to c:\program files\common files\research in motion\apploader and delete the file named "vendor.xml." Also check the following locations for vendor.xml files and delete any instances of the file:
On Windows Vista/7 navigate to C:\Users\YOUR_USER\AppData\Roaming\Research In Motion\BlackBerry\Loader XML (Where "YOUR_USER" is your username)
On Windows XP navigate to C:\Documents and Settings\YOUR_USER\Application Data\Research In Motion\BlackBerry\Loader XML (Where "YOUR_USER" is your username)
5. Use BBSAK from BBSAK.org or JL_Cmder
and wipe the device (after doing a complete backup) then after you get the error 507 (no OS installed) then proceed to next step.
6. Plug in BlackBerry and double click on "Loader.exe." It's located in c:\program files\common files\research in motion\apploader