Are you able to restart your device in safe mode as shown in KB17877-How to start a BlackBerry smartphone in Safe Mode
I assume, since it's caught in a reboot cycle, when you connect to the Desktop Software it doesn't take a stable connection to reinstall your software?
If that is case, remove your battery and keep it out when you connect to the Desktop Software. You will get a pop up that the device can't connect and there should be Retry, Update and Cancel buttons. Select Update and you will then be able to reinstall the current device software version.
When the load is progressing, you will see a step that says "Wait for device initialization". At this point, insert the battery and the reload should complete.