When you reinstall or reformat an OS you will usually need to completely install every device driver. These can be found at your manufacturer's website. if the computer is a Dell or a brand name, virtually everything you need can be downloaded from their support locations using the service tag or model numbers.If you have a custom built computer it can be more difficult and you will probably have to track down each device individually. I would recommend you start with the motherboard, as this will often include, chipset, usb, audio, networking, and video drivers. This is the bulk of your missing software. If you don't have brand name support, find out the name of your motherboard, consult the manual or physically read it, go to their website> drivers and technical support > and using the motherboards manual locate the software for your specific device and download the drivers for the appropriate operating system.Note: You will need to repeat this step with every piece of hardware that you need to install.