If you look something to customize your pc's sounds you can use easily wav sounds. You could for example use the files that you can find easily on this website: http://www.ilovewavs.com/. Just scroll down until you find windows events.
I could recommend other sound sites, you try for exemple this page for windows events sounds, but you could try aswell this request in your favorite search engine that gives probably better results that "sounds for my pc".