Find the key with the image of a pointing finger (often it is F7). Press it and Fn at the same time to make sure that your touchpad isn't turned off. If that isn't the problem, do it again to make sure that it is turned on.
If that doesn't work, restart in Safe Mode and try it. Get into Device Manager and see if your touchpad and your mouse are working properly--mouse software MIGHT be messing up your touchpad.