Hi,
I know you said that you searched everywhere. Did you look in Device Manager?
Go to Start > Control Panel > Hardware and Sound > Device Manager > Imaging Devices, expand tree and see if a camera is listed there.
If it is, but there is a red cross or a yellow exclamation mark next to it, either enabling it, uninstalling/reinstalling it or updating the driver for it may solve the problem
If it is not listed, it could be a hardware issue, a loose Webcam connection perhaps.
The Webcam is usually at the top middle of the laptop lid and the connector might have become loose with repeated closing and opening of the laptop lid. Gently press together both sides at the top middle of the lid (both sides of webcam - with thumb and forefinger) and the loose connection may reseat. Watch, as you do this, for a notice on the lower right of your computer that a New Device has been found and that a driver is being installed - or something along those lines. Then check to see if your Webcam now works.
If it still doesn't work here is a link which shows how to remove the screen for a Lenovo T400. Admittedly it doesn't have a webcam, but it might show enough how to get access to one if it were there, so that you can either check the connection or start to replace the webcam.