no sound on xbox 360

I bought xbox 360 e from amazon it's been 1 month ago,it's working perfectly, then i update the system for xbox 360 live account it's updating through internet, then my internet cut off during the update download then screen goes black and i restart the xbox 360 then everything back to normal then i realise no sound and i restart again sound is back, now it happen sometime, it's the update failed causing no sound or the hdmi.