my brush size icon won't change

hi,

I have photoshop CS6, on a  iMac OS x version 10.9.4 .  I am having trouble with my brush sizes,  when I enlarge my brushes they only get so big before the icon stops growing,  the brush function gets larger but the circle that shows the edge of the brush doesn't.  I opened my photoshop in default, that didn't work, I called apple, they didn't know what the problem could be.

I don't know what to try.  Has any one had a similar problem?

Millie