Did your computer come with a setup DVD? That setup DVD may contain crucial drivers
for your computer including the ones for sound and network. So use that and check it out if your computer came with a setup DVD. You may need to ask at the store you bought that machine while its new.
If not, here's a solution. Type Device Manager on the Search bar st the Start Menu. On the Device Manager, under "Network Adapters", choose your network adapter, right click it and choose Update Driver
Software. Then Browse My computer for Driver Software then Let me pick for driver software installed on my computer. It shows a list of compatible driver software. Click one until its highlighted and choose Next. It should try installing driver software then you may need to restart for that to take effect.
If this won't do either, copy the exact name of your motherboard. Use another computer with Internet, type that name on Google and add "ETHERNET drivers for" lets say for example "ETHERNET drivers for <exact name of your motherboard model>" then Search that on Google. You can see links where you can download drivers for that, look for the ETHERNET driver compatible for Windows 7, download that, put that on a USB drive then install that to your computer.