I use a MicroSoft IntelliMouse Explorer. But I've seen this same problem with other wheel mice. You often - & for no apparent reason - loose the ability to zoom with your wheek button. Here's the fix:
Get to your MOUSE PROPERTIES dialog box...
START > SETTINGS > CONTROL PANEL. Under the WHEEL tab, in the WHEEL TROUBLESHOOTER box, click ADVANCED. Then DISABLE ALL INTELLIPOINT SOFTWARE WHEEL SUPPORT... Add SolidWorks to the list of programs. (Might as well add SolidWorks Explorer & E Drawings too.)
Apparently, SolidWorks manages the wheel & will conflict with the Microsoft mouse drivers... go figure.
