A bit of a disclaimer: I hate networking issues and I'm not too well versed in Windows' networking. Going to do my best to really learn networking this year in particular, so I can resolve a lot of these issues in the future.
That said, the first thing I would do is, check your network connections. You can do this by going to Start>Control Panel>Network Connections. It should show you two sections, Internet Gateway (whether you're connect to the Internet or not), and LAN or High-Speed Internet, provided you have an Ethernet card in there or if it's part of the motherboard's chipset. If you highlight and right-click on the Wireless Network Connection, you can select View Wireless Networks to see what's available and if you're connecting to any of them or change them, you can use Status to see what's going on with your network connection, and you can use Repair to try and see if that remedies it.
The other thing I would recommend in particular is checking Device Manager to make sure all your devices are working okay, namely your ethernet/LAN connections. You can get to Device Manager by right-clicking on My Computer, going to Properties, clicking the Hardware tab, and selecting Device Manager. If you see any devices with a question mark and/or exclaimation point in a yellow circle next to them, you have probably have a driver issue; in which case, you'll want to either find a way to get on the Internet and go to the manufacturer's website of the device to get the latest drivers, double-click the item and see if Windows can find a driver for it (although this requires the Net), or just see if you have the CDs that came with the device.
If they both used to work though, I imagine it's a network issue and not a driver related one,
