OK, that gives us something to work on.
Odds are it's miswired. Here's why I say that. First off,
here's a link to your manual. You might want to check it out carefully if you haven't already.
You have a fairly unique situation in where it's brains are in one unit and it's muscle is in the subwoofer. Both are connected by a propriatary cable. If you ever lose or damage that, you're probably screwed.
The crux of the matter is that you can use
ONLY the subwoofer that came with this system. It
CANNOT be replaces with a differet subwoofer.
So, I'll assume you have that propritary cable and the subwoofer that came with the unit.
To start with, I'd unhook
all the speaker wires from the subwoofer and then, very carefully, reconnect them and reference the owners manual if needed.
Remember, each speaker wire has a matching pair (illustraion shows black/white) and they must be plugged into the same matching connections for the same speakers on the subwoofer. If you put the speaker wires in the wrong holes on the subwoofer, anything could happen.
Once you've done that and you're positive that they are correct, and the unit still does that weird shiite, then there's a problem with the unit and service will be required.
Still, my $$ are on a miswire. It's an easy mistake to make, particularly for a newbie.