No sound from my external speaker?

i got a used iPhone 1st generation from my uncle several months ago, and it's worked fine up until now. i am able to hear certain things out of my external speaker, but everything else does not make any sound. i don't have my ringer on vibrate, so don't even try saying that's the problem. i cannot hear my ringtone, music (with no headphones plugged in), or even that little clicky sound it makes when you unlock it. when i call someone or someone calls me, i cannot hear them and they cannot hear me. there is only sound coming out of the external speakers (the ones on the bottom of the phone) when i'm setting a different ringtone or when an alarm/timer goes off. i would like to be able to use my phone; can someone please help? thanks(: