why can't i hear sound? and how do i fix it?

so i have had trouble with gta 5 downloading it and  it works fine but there is no sound....

i looked at the s ound settings and i saw that gta v had a grey line in it? what does that mean and how do i fix it???

https://cdn.discordapp.com/attachments/778870139185266701/791942342432129054/unknown.png

cheers and merry xmas :D