mobile

Hello! I am posting this because I have searched for hours on how to fix the phone with no luck, so this is a last resort. Im using a AT&T (sadly) galaxy s5. I was going to update to lollipop but couldn't since my device was rooted. I tried to unroot it by using supersu, but pulled the battery because it was taking forever (I know I know.) The phone at first booted to safestrap and I tried to factory reset to take off the root. Now, whenever I turn on my phone, it wold be at the samsung galaxy s5 screen with the little unlocked symbol. I tried to flash the stock firmware with odin. Didnt work. Now it boots (still says unlocked) and when the samsung animation finishes, it stays on a black screen. Any help at all? Thanks!