Take a look at this guide if this does not help then you may be looking at faulty hardware, and it may be time to check the warranty.
Here is the condensed version:
1) Make sure you have Blackberry Desktop Manager installed.
2) On your PC, go to Start > Run and copy and paste the following line exactly:
c:\program files\common files\research in motion\apploader\loader.exe" /nojvm
3) The Application Loader Wizard will appear -- click "Next."
4) In the "Connection:" drop-down menu, you should see "USB-PIN: UNKNOWN". Click the "Next" button.
5) You should then see a list of applications ready to be installed for your BlackBerry. Hit Next and Finish and you are well on your way to getting your Blackberry back to life. Just don't disconnect anything and let the lengthy process finish completely.
If you do not see the list of applications in step five then you need to download an OS for your device.