Internet is gone, cant get back

Hello,
I have recently got my comptuer fixed because the power supply was faulty, I brang it home and connected everything and started the computer everything worked fine but no internet, in the network connections their is no connections. I run a Windows XP my network adapter is Realtek RTL8169/8110 Family Gigabit Ethernet NIC, i tried Rollback and it said it cant rollback, i tried Uninstall and i couldn't uninstall it , it said "This device may be needed to boot the computer". I dont know what to do please help me :)