If your sink won't turn off, there are a few things you can try to fix the problem. First, check to see if the problem is with the handle or the knob. If the handle is loose, tighten it with a wrench. If the knob is loose, tighten it with a screwdriver. If the handle or knob is tight, the problem may be with the valve. To fix a valve, you will need to remove it and replace it with a new one.