Have you tried pressing Fn + F7 together to 'toggle' the touchpad back on? (Fn + F7 turns the touchpad both On and Off)
Where did you check in Device Manager, was it under Mice and other pointing devices?
Also have you checked in Control panel > Mouse to see if the touchpad has been disabled there at all?
What OS is installed?
Just a thought, see if the following is available
Go to Mice and Other Pointing Devices in Device Manager and see if there is a listing for a USB Touchpad controller.
Right click on the listing and select Update driver. When you get to browse my computer, you'll have the option to "let me choose" and then you select "usb input device" instead of "touchpad controller."
Also have you checked for 'hidden devices' in Device Manager, (located in the View tab option)?