strange problem

[SGWills]

i keep getting a strange ummmm, i suppose its an error really, it normally happens with a window that is not maximised however it does happen sometimes when it is maximised, i will go to click a link or use an action in photoshop say, but my pc will act like nothing there, i.e will select something on the window behind, click maximise but it will deselect the page, its an odd one to explain but its getting on my nerves, any ideas ?