|You probably DID NOT need to re-load Windows.|
You probably have a hardware problem, NOT a software problem.
If this is with an external (USB, PS/2, or wireless) mouse, try a different mouse.
If this is with a touchpad on a laptop or netbook, try an external mouse.
If that doesn't help....
Tell us the make and model of your brand name system, or if you have a generic desktop system, the make and model, or at least the model, of your mboard.
The model of a brand name system is usually on a label on the outside of the case,
or if it's a Dell system, go here to find your Service tag number, tell us what it is:
The model of a mboard in a a generic desktop system is usually printed in obvious larger characters on the surface of the mboard, often between the slots, or near the center of the mboard.
Some computers show a screen with the model number on it while booting the computer.