There might be a way to go back I think but it's means flashing your ROM.
If you haven't tried a soft reset, try that first. Volume down and power button until phone vibrates then let go.
Next option is to try a hard reset. Settings -> About -> Reset phone.
This will wipe everything from your phone so be sure to backup.
Last option you can look at is using this (requires PC):
http://forums.windowscentral.com/win...very-tool.html
It will install a fresh firmware. It will completely wipe everything from your phone.
I'm guessing your firmware got corrupted somehow but I can't say that for certain.