Sounds to me like a bad install.
Originally Posted by Deano09
Did you try removing the theme via Cydia or can you not click anything to do that?
If that doesn't work or you aren't able to access Cydia to uninstall the problem package you may have to restore and re-jailbreak as a last ditch solution.
As a side tip, always make sure packages are compatible with your version of iOS. I've seen it create numerous issues. Especially be careful on iOS 5 as a lot is NOT compatible yet and can cause crashes and freezes.