@jacob1 got it all wrong, using the scrollwheel or [ and ] only changes the size of the brush. He probably didn't read your post correctly.
Anyway, it's better to post a screenshot (Upload it using http://imgur.com if you don't know how to upload images). If you don't know how to take screenshots, there is this indirect method using Steps Recorder (you have it by default, just open the start menu and search it): http://i.imgur.com/YhytL7Z.gif
Or if you have a good screen capture program that shows the cursor, use it I guess. The reason why you shouldn't use the good old Print Screen method is because that one doesn't show your cursor.
Edit: You don't have to register to upload images on Imgur.