It is possible that the window that you are trying to scroll in, is not the active window or that the cursor is not on the page.
For instance. If you have Safari/Firefox/insert your browser of choice open and the cursor is outside of the page area, the Scroll Wheel action does not happen.
The fact that your scroll wheel (button) works when the cursor is placed over the blue scroll bar would indicate that there is nothing wrong with the mechanics of the mouse.
Next time it happens, check to see if the cursor is inside the window you are trying to scroll.
If it has been a while since your last restart, try restarting
Let us know
For the last couple of days my scroll button on my Mighty Mouse doesn't work any more. I've looked it up and see nothing about not bring able to scroll at all. Yes, if I put the pointer on the blue scroll BAR it works..but liked being able to scroll from anywhere in the screen. Any suggestions, thanks to one and all
2.16 Ghz Intel Core Duo IMAC 20", wireless keyboard and mouse