Missing Ethernet after erasing and reinstalling Snow Leopard

I bought a Mac Mini in 2010. I don't remember it coming with an install disk nor can I locate it if it did. My dad loaned me a copy of his Snow Leopard because I needed to erase my hard drive and reinstall Snow Leopard. I backed up all my files and everything seemed great until I tried to connect to the internet. I have no ethernet in my network preferences. The only way I am able to connect to the internet is via the Net Gear router that is connected to the modem. Without my router I wouldn't have internet. I have removed the router from the situation and tried directly plugging the ethernet cable from the modem to the computer with no success. I have rebooted the modem and the computer with no success. Please advise & thank you! 😀