Most systems with an Intel Core 2 Duo E8400 are older desktops or laptops that use third-party audio chipsets (Realtek, Conexant, VIA, etc.), not Intel-branded onboard audio. That means the right driver depends on your motherboard or laptop model, not the CPU. Follow these steps to find, download, and install a working audio driver.
Windows + R, type msinfo32, press Enter.Intel Driver & Support Assistant: For Intel-branded motherboards or NUCs, use the Intel Driver & Support Assistant to automatically scan for and install compatible drivers.