I have an IBM ThinkPad T23 and have installed XP Pro with a Product Key (non-OEM). When the laptop lid is closed, the laptop does not go into Sleep mode. When I access Power Options under Control Panel then click on the Advanced Tab then click on the drop-down under "When I Close the Lib on my Portable Computer": the only option is "Do Nothing". On my other ThinkPads there is an option to choose "Sleep". What is to be done to access sleep mode on the T23?