no sound pc windows 10

Have a gaming PC - cheap - have speakers. gaming headset. I cannot see a problem, but still there is no sound. Occasionally we can hear 'playback' other players on the game or music. Than I do something and all sound vanishes again. I sent the seller photos and he says I must put in the name of the headset - I have no idea what his instructions are actually, I don't know what I'm doing. So I bought a splitter and have tried it in the from and the back of the tower and everything tests fine but still no sound.