Well, this is an S3 forum, but:
First thing I'd try is a battery pull. Shut it down, pull the battery for a few minutes, then try again.
Is your phone rooted? Have you disabled any apps (in the Application manager - if the S2 has this capability), or frozen any apps using a program like Titanium Backup?
Did you install or uninstall any new apps shortly before this started happening? Were you using a different launcher, and tried to switch back to TW?
Without a little more information, it's hard to suggest anything specific.