My computer speaker has a problem with the bass knob. The bass is hard to balance because there were times when the bass will be totally gone when I adjust the knob. It is like picking a locked door, turning the picks slowly to get the right position in order to open the door, the bass in the case of my speaker.
How old is your computer speaker? If it is fairly new, then better send it back to where you purchased it. If it is old already, then it may be wear-and-tear, so I recommend that you purchase a new one or have it repaired.
The speaker is old, but it is still working fine with the bass knob the only problem it has. I made a silly, but effective solution to this problem. I inserted a piece of paper in the gap around the knob for the knob to stay in place.