Probably the ‘sound’ control in IE is on mute or low.
In IE, load a video and check to see whether the volume control is on mute to very low.
Since you are getting sound through other browsers, it sounds like an IE situation.
I have that occasionally, as I run several different browsers.
Some computers will allow you to mute video feeds individually, while others will mute everything if ‘muted’.
There’s no sound control at all. Not even the icon.