If you are trying to connect through a modem/router you it should have come with a disk then
you might have to connect the usb lead to your modem to get a connection then
click start control panel,administrive tools,computer management,device manager scroll to network adapters should see a yellow question mark? right click install drivers
the driver might be on the disc supplied by your ISP internet service provider
or the motherboard disc
hope this helps or you could download
Realtek RTL8168/8111 PCI-E Gigabit Ethernet NIC http://download.cnet.com/realtek-rtl8168-8111-pci/3000-2112_4-99235.html Realtek RTL8168/8111 PCI-E Gigabit Ethernet NIC: The Realtek RTL8168 Gigabit Ethernet controller combines a triple-speed IEEE 802.3 compliant Media Access Controller (MAC) with a triple-speed Ethernet transceiver, PCI Express bus controller, and embedded memory. With state-of-the-art DSP technology and mixed-mode signal technology, it offers high-speed transmission over CAT 5 UTP cable or CAT 3 UTP (10Mbps only) cable. Functions such as Crossover Detection & Auto-Correction, polarity correction, adaptive equalization, cross-talk cancellation, echo cancellation, timing recovery, and error correction are implemented to provide robust transmission and reception capability at high speeds.
hope this helps