Menu bars don't change directly when I click it

[mystvearn]

I don't know how this happened in the first place but here goes.
I have lots of windows, Firefox, messenger, windows explorer all open and you can see it on the start panel bar. When I click the bar once, it does not become active directly, instead I see the bar flashing. I have to double click it, which minimizes the window, and click on it again to make the window active and on top of other windows. This is annoying. How do you fix it so that when you click once, it becomes active and on top directly?