I'm guessing the battery pull isn't going to help. Hope it does, but if not, here's some things to do.
1 - You'll need desktop manager installed on a computer you have access to. If you don't have desktop manager, go to blackberry.com, download, and install.
While you are at it, think about what apps and themes you have recently installed. Try and remember what was last, what before that, etc.
2 - You may want to go ahead and download and install JL_CMDER. You may not need it but go ahead and get it done. You'll find out how to to get it and how to use it at BlackBerry FAQ - BlackBerryFAQ
3 - Remove the battery again. When you replace it, and just as the device begins to boot, hold back/esc key for several moments. The device will hopefully boot up in safe mode. I'm not sure how critical timing is, but I was able to do it first try. If you don't get it, try again. Search on safe mode if you need make sure you are doing it right. If you can't boot up in safe-mode, then go straight to wiping with JL_CMDER and resinstalling the OS.
EDIT: Here's the documentation on safe mode: http://www.blackberry.com/btsc/dynam...C&kcId=KB17877
4 - If you are able to boot in safe mode*, then start desktop manager and connect the blackberry. First, do a backup. Then disconnect the blackberry and see if you are able to open options and delete applications. If so, then delete the application that you last installed; if you are not able to do this, then connect to the computer again and run the application loader/unloader utility in desktop manager and see if you can remove the application that way. If you suspect a new theme could be the problem, then same thing, remove it.
If you are unable to delete applications, then hopefully you were at least able to backup, and the next step is to just wipe with JL_CMDER, re-install the OS, then restore you data and apps.
If you are able to boot the device, then it would appear you solved the problem. Use the device for a while and see what happens. Or, play it safe and wipe the device with JL_CMDER and resinstall the OS and then restore your data and apps.
* Caveat: I have not actually done this before. I have been in your spot, but it was before I learned about safe mode. But I think this will work. Plus, safe mode should at least give you the opportunity to do a back up...hopefully.
Good luck. Post what you find if you do try this.