Whether you need a computer for your child to use for schoolwork and entertainment, or you want to save some cash and keep a laptop out of a landfill by resurrecting an old one, you have a few options.We’ll walk you through updating an old computer that has been sitting in a closet for years. The newer the computer you’re trying to revive, the easier it will be to reuse, but even eight- or nine-year-old computers can be useful if you’re just trying to get by.If you do have an old computer collecting dust but don’t know how old it is, do a Google search for the manufacturer name plus “serial number lookup.” The manufacturer’s support site may let you enter the serial number (often in the fine print somewhere on the computer) and show you its model name and number, when it was made, and what operating system was originally installed on it.