If I understand correctly, you recently reinstalled Win7, because of the exact problem you are having now. So, I'm just wondering, since it was apparently working and then it wasn't, you reinstalled and subsequently it was working and now it isn't, if an intentional or unintentional hardware driver update either by you or by Windows Update may have resulted in your present predicament.
You could always maybe attempt a driver roll back from within device manager if that is an option.
I'm not certain that yet another reinstall of Windows 7, wouldn't, sometime in the not to far distant future find you right back to where you are now.
Is there anything peculiar about the surface that the mouse in on, some grained surfaces, reflective surfaces or transparent surfaces can produce unexpected behavior.
On the whole, I personally have not had very good experiences with wireless keyboards and mice, especially blue tooth and laser, they are a heck of a convenience when they are working properly, but often not worth the pain. I have resorted back to wired for reliability, when I click I want something to happen and when I strike a key, I don't want to have to wait.