No need to format anything. You can actually use an old windows installation for a new PC but it is not recommended as it can cause problems. The easiest way to find the problematic part is to remove all stuff that isn't needed to go into the bios screen(HDD, DVD-ROM). After that reset the bios either with the button for it(if there is one) or by removing the bios battery for a few seconds. Then you might want to check if your GPU's fan spins up. You can also try a different PCIe slot for the GPU. Make sure all power inputs on the mainboard and GPU are connected. It might also be a loose contact so try moving the connectors a bit when the PC is off.