My jailbroken iPhone 3G has a glitchy screen and will not unlock

Details on iPhone: Type: 3G Version: 4.2.1 Modem Firmware: 6.15.00 Service Provider: AT&T I recently jailbroke my iPhone 3G using Redsn0w version 0.9.6b6 for 4.1/4.2.1. When I performed this I checked "iPad Baseband" as I was told. When all this finally finished my iPhone rebooted but I noticed the screen would flash transparent white bars horizontally. Is there a source from Cydia I can install to get rid of this?????? And yes, my screen was perfectly fine before the jailbreak.