4. Both mouse and keyboard are PnP devices and require drivers. Every time your computer boots, it scans all the devices and looks to see if drivers are installed. If it doesn't find the driver, it snatches one from the CAB files and installs one.

This means that if the PnP identity of a device isn't read correctly, a new and different driver may get dropped in place.

Many drivers can be "modified" during computer use, as when you change the scroll rate, mouse-click/double-click separation etc. The changes generally get written to a .dll script, but since the mouse uses a sepcific script that the driver looks for, this can result in a "corrupt driver." This is fairly rare, but can happen so one must assume it does.

The solution here usually is just to uninstall the driver and then reboot and let Windows pick and install a new one. In Control Panel, double click either Mouse or Keyboard, on the Hardware tab click Properties, click the driver and then uninstall. Reboot.

NOTE: Never change more than one thing at a time when you're trying to get something fixed.

NOTE: If the mouse quits working when you uninstall the mouse driver, it means you've done what you came for, so don't worry about not being able to back all the way out of Control Panel. You can do it with just the keyboard; but Ctl-Alt-Delete will open Task Manager, and a second Ctl-Alt-Del should shut you down so you can restart.

John