Mouse drag select PROBLEMS... plz hlp

[pyroxene]

My problem is thus...
If I left or right click my mouse and hold and drag (like as if I am making a box to select mutliple icons) my mouse pointer turns into a circle with a slash through it (like a "you cant do that you dummy" icon).
Now this only happens on my desktop. If I try to drag select several icons in a folder it is fine.
Also, if I click my mouse and drag it off the screen (like moving it far to the left or right) then it does a double beep noise and then the mouse locks on the circle with the slash until I move it around abit then click a few times.
This is happening on a corded optical mouse (also did it with my roomates corded optical). Thnx for any hlp.