Hey there, same thing happened to me.
But fortunately, there is a fix!
On the power Socket of the sub8 speaker( where u stick the power cable in the back of the speaker)
There is this little cap right underneath the Socket.
U can pop it open with flat screw driver. It's a small fuse box. And inside u will see the burnt fuse!
But there is also a spare Fuse in the small fuse holder.
So u just replace the burnt fuse with the spare and that's it.
Just make sure, to have the speaker plugged out and turned off while doing this.
Hope this helps anyone with same issue.