After 3 months of no sound, and trying EVERYTHING suggested on these pages, I have finally fixed the problem!
I bought an iPhone 4S USB charging port dock block connector for under a fiver off eBay, and got a friend to remove my old one and put the new one in, just by following a video on youtube!
I tried cleaning the docking port as suggested, blowing in it, using compressed air, switching the do not disturb button on/off, restarting/rebooting, asjusting every single bloody setting on the phone and I even took it to the genius bar (who weren't much help) just wanted me to pay over £100 for new part)
Turns out the red indicator was on which means it's water damaged (even though I never take my phone into the bathroom and even have a special case for my phone which protects the docking area).
But now my phone works perfcetly, I have a ringtone, message tone and other alets and I can listen to music and watch videos now without having to have my headphone in...YIPPEEE! I cannot tell you how happy I am!!
Surely apple should design a phone that doesn't get water damaged so easily???
Anyway, hope this helps you!