Why won't my sound work?

Ok, i will start of by saying, MY PHONES SOUND DOES NOT WORK…..

I got my iPhone 4 in 2013, it was a hand me down from my dad. My dad has never every spilt anything on my iPhone. I have regularly updated to the latest software, cleaned the screen and took good care of it. Anyways, lemme get to the point, I can only listen to things on my iPhone when i have headphones plugged in. The volume worked fine when the headphones are plugged in, but when i leave them in for a long period of time, for example, overnight, the sound won't work. Without the headphones in, i cannot listen to anything, accept my alarm and ringtones. Music doesn't work and the volume icon doesn't even show up when i press the buttons. At times it will work for like, 3 seconds, but it doesn't work in general. A while back, my mum found my phone on the floor of my bathroom, and tried to pick it up and give it to me. but, when she tried to pick it up, it fell maybe a inch to the floor and the screen cracked. A while later my water bottle spilt in my back pack, but it was fine after my mom out it in uncooked rice over night, and now the sound doesn't work..