Speakers + subwoofer: the second one does not work. How to fix?

Question

Do it yourself

Guys. Such a disaster happened. I have an old sub in my hands. He is exactly 10 years old. Everything was working great until last week. I had to give it to my brother for a couple of days to use, and when he brought it and I tried to listen to music, I did not hear the bass. The speakers work but the subwoofer doesn't. Shows no signs of life at all. If the speakers hiss when turned on, then such a buzz is not observed with the sub.
My brother says that he just stopped working ... But something tells me that he is lying, because when I began to inspect the subic in detail, I noticed that the channel switch button (BAND button) when pressed, can switch immediately to 2 or 3 orders ... and Still on the case, traces of an attempt to open it are clearly visible.
It doesn't smell like burning, I checked. But this is the only thing I could check) Well, I also superficially examined the insides in the hope of finding something and sorting it out, but I don’t rummage.
If someone can tell me how to troubleshoot, I will be very grateful.
Subwoofer SVEN
Model: IHOO MT 5.1
Power 35W
Power supply 220 V, 50 Hz
PS: Someone on Skype or Google Tangouts will explain and show...

Answer 1

I had to give my brother a couple of days to use

They gave it whole and it worked.
Does he care what, how and why? Take the whole - return the whole.
The choice is either the brother pays for repairs, or brings a new device, and this one takes it for himself.