I would use the second one but not the first one. (Music doesn't play itself.)1-When I went there music played in the background.
2-When I went there music was playing in the background.
"When I went there a big mirror stood in the cormer of the room" suggests that a mirror was doing something mirrors don't do (stand). "When I went there a big mirror was standing in the corner of the room" has the same problem as the previous sentence. However, "When I went there, standing in the corner of the room was a big mirror" puts the mirror in its proper place.