remove cm 12 nightly from phone

i recently flashed the cm 12 nightly rom to my lg g3 rooted att phone..
i can no longer go into recovery mode and when i turn off the phone,i need to remove the battery and re insert it in order for the phone to start again..
i would like to remove this rom and replace it cloudy rom,but i can't get the phone into recovery mode...message says i need root access...help!! i am new at this