When you start your computer using a WinPE (Windows Preinstall Environment) image that was built in a Windows XP SP1 environment, the USB 1.1 devices, including your mouse and keyboard, do not work.

This behavior occurs because the USB driver stack in Windows XP SP1 was changed so that a USB 2.0 host controller is started before any one of its' USB 1.1 companion controllers, to avoid conflicts when enumerating companion USB 1.1 controllers.

WinPE loads all the required devices drivers as boot devices. If a USB 1.1 companion controller is not started within ½ second of the USB 2.0 controller, it is not enumerated, and will not function.