Most scrap yards will purchase scrap electronics, including computer towers, laptops, and computer components.  It is better to sell laptops whole, as it takes too much time to remove individual components.  As for computer towers, these are easier to break down, but only suggested if you have a large number of units.  You can separate components, such as motherboards, hard drives, CPU's and sell them separately.  If you have 1-2 computer towers, it is not worth the time to break them down, you can sell them whole.