Samsung Galaxy S4 system update crash - can't use phone at all.

A

AC Question

Hi everyone, my name is Sarah, thanks in advance for helping me.

I woke up this morning to find a system update was ready to install, so proceeded as usual. I've had this phone a very long time and never had problems with updates before. Everything seemed to be fine, but I will mention now the volume key on my phone is broken. I can easily turn the volume up, but where the down key is, the button has dented in for some unknown reason and I can't use it. However, whenever I want to turn the volume down, I just press the up volume key and use the slider on the screen to turn it down.

Anyway I come up with this message on my phone during the update:
"Warning!! A custom OS can cause critical problems in phone and installed applications. If you want to download a custom OS, press the volume UP key. Otherwise, press the volume DOWN key to cancel."

So yes you can see where my problem is! My down key is broken and I can't press it. However I pressed the up volume key, and nothing happened. I pressed the down key as hard as I could, and the screen basically refreshed and went back to the same message. So I can't seem to get anywhere with pressing either buttons! So then I turned my phone on and off, still went back to same screen and message. I took batteries out, sim card and memory card. Waited 5 mins, put them all back in, and again back to same screen when I powered up.

I'm really annoyed and have no idea what I'm doing! So please, some kind stranger, help a young girl who knows absolutely nothing technical about phones. Thank you!