To start, go to Control Panel and click on Mouse. If you are in category view, click on Hardware and Sound and then click on Mouse under Devices and Printers.
In the Mouse Properties window, click on the Hardware tab and select your mouse from the list of devices. Normally, there will only be one mouse listed here, but that will depend on the hardware you have connected to your computer. When you have selected your mouse from the list, click the Properties button.
In the second Properties window for your mouse, click on the Change Settings button on the General tab.
Finally, click the Power Management tab and uncheck the Allow This Device to Wake the...