zero neck
The Ever-Living
Did you wipe cache partition, dalvik cache, and full data wipe before you flashed the rom?
What rom was it?
What you need to do now is pull the battery out, wait a minute, put it back in, reboot into hboot (volume down plus power button), select recovery with volume keys, press power, then when it boots into recovery, navigate to backup and restore, select by pressing home key, select restore, and select your back up and press home key, then reboot.
this will get you back to your backup and things will be ok, and you can try to flash the rom again after that but make sure you wipe those things first or it will not work properly.
What rom was it?
What you need to do now is pull the battery out, wait a minute, put it back in, reboot into hboot (volume down plus power button), select recovery with volume keys, press power, then when it boots into recovery, navigate to backup and restore, select by pressing home key, select restore, and select your back up and press home key, then reboot.
this will get you back to your backup and things will be ok, and you can try to flash the rom again after that but make sure you wipe those things first or it will not work properly.