1. I would remove media card.
2. unistall current deviceOS from your PC
3. DL and reinstall a fresh copy of the lastest
OS to your PC.
4. pull the battery.
5. go to c:\prog files\common files\Research in motion\apploader and run loader.exe let it go through the complete process. your device will reboot and you will get 507 error on your screen.
6. put the battery back in
7. repeat step 5, this time you wont get 507 error
hopefully that helps