Ok so here is the problem:

I updated my phone I927 to ICS via Kies but it is laggy and doesn't load some major things like keyboard and stuff. So I thought I should downgrade so I grabbed the GB firmware and flashed it. Odin said everything has succeeded but the phone doesn't go further than welcome screen. :-/ Any help? Tried Wiping through recovery after flashing GB.

Replies will be highly appreciated.