Hi @SnehaBinu, I'm sorry to hear this. 
I recommend that you test the loud- and ear speaker in Diagnostics. This would help us determine if this appears to be hardware or software related.
You can find Diagnostics in Settings > About phone. In Diagnostics you then tap on Tests and run the tests for the different speakers.
Let me know how it turned out once you've been able to test this.
@SnehaBinu wrote:Suddenly today my Sony ultra C5 went dumb .. i.e. no sound coming from it... Even while playing games or calls or playing videos.. no sound is coming ... It's completely silent..I tried a lot but still it's silent.. Plz help..!
I just want to supplement little Christofer, in my Xperia C5 Ultra Dual when i had Lolipop 5.1 diagnostic app did not detected sound, but everything was fine with soundspeakers and ect., so diagnostic app didn't showed 100% trust results for me, so don't reject possibilities just to repair yours smartphone with Xperia Companion, if will not helps repair bring yours smartphone to authorized service in your location for professional diagnostic where will be test yours smartphone with professional technique 
