Try maybe work!
1) Desinstall RobloxPlayer.exe
2) Look at your computer sound at right down on your computer desktop and then go mixer and then found RobloxPlayer and check your sound!
3) Look at your sound in roblox game "Volume"!
I dont know if it doesn't work im sorry :(
Try turning up ingame sound, if that doesn't work.
If that doesn't work, go to Control Panel, siwtch to small Icons and go for the Sound setting.
Uninstalling Roblox is pointless, so you want to avoid that for this case...