This is SO freakin' aggravating!!

What is the key combination to make the stupid mouse cursor STOP scrolling
sideways? (And no, it is NOT anything involving the ScrollLock key - I not
only didn't hit it to 'turn something on', but after trying it alone and with
every stupid key on the kb, it does NOT turn anything off, either.)

I will be working in Excel on something, and for no reason I can find, the
mousewheel suddenly will only make the cursor scroll sideways! The only
mention I can find in Excel's help is to press the wheel to make the little
4-headed arrow icon appear, then roll the mouse in the direction I want it to
scroll . . . except, of course, that only works if the 4-headed arrow icon
will actually appear. When this starts, I can only get a 2-headed arrow icon
.. . . the horizontally-pointing arrowheads, of course.

HELP!!!!!