3 or 4 times a week my MacBook laptop freezes. When this happens, I can move the cursor around the screen but I cannot click on anything, or change anything on the screen. So I have to force quit by keeping the power button pressed down and then start up again. The screen freezes when I am on the internet and clicking on something - like making the screen larger, or opening a site within a highly trusted site, or something else. I called my internet service provider and there is nothing wrong with my line. Any ideas?