If you are saying that you have a scroll bar, but cannot scroll, you seem to misunderstand some basic principal about how the mousewheel works. Your explaination trails off into garbled mush when you say that you can use your mouse to scroll...
OOOOOH I did not understand. When someone talks about using the mouse, I think only of the pointer thing, because I use a laptop. You meant that you use the mousewheel to scroll. Yes, mousewheel sensitivity is low in blockland. If the side of your screen is cut off there, you can reset that gui, change the resolutioin of blockland, move the gui a little over, or resize the gui so it fits.