Do any of your keys have any icon on it that looks like a mouse or a mouse with a line through it? Try that key (might require you holding the Fn key, too)
If it's an older or well-used touch pad, it might just be that it has broken, and you might need to get it repaired in a shop.
Down in the right corner by the clock you should have an icon that looks like (the square with two smaller squares under it - might have to click the arrow to show more icons to find it)
Right click on it, click on pointing device settings (or whatever opens it). It brings up device settings...