1)when you reboot the pc press ctrl. alt. del. keys to open task manager and check the process tab for anything using a lot of cpu as it could be some malaware or virus/trojan etc.
2)If you can't see any process that looks dodgy in task manager try opening device manager. control panel>system>device manager and expand the + keys to examine any driver problems for your hardware. if you think the mouse is starting the problem then EXPAND human interface devices and check out properties on the mouse.