The key word you used is "mouse". This problem is usually caused by hardware issues, especially keyboard/mouse. Go to your Mouse Properties, either through Control Panel or Device Manager, and look for the Power Management tab and take the tick out of "Allow this device to bring the computer out of standby" or similar. This means you will have to use the keyboard to waken your laptop.
If it doesn't work do the reverse to put it back the way it was.
You will probably need to do a restart for it to take effect.