Since you can access the net through your router with other devices, it looks like there's something fishy in your computer, if I have understood your message correctly.
Now I don't know your mileage with computers, so this 101 may be too detailed for you but just the right thing for another someone:
1) Reset your IP stacks and other NIC related things. This is rude and simple but it works: Go to Start->Control Panel->System->Devices->Device Manager or simply type "devmgmt.msc" without quotes in the search (or run) bar. Find Networking devices, expand it with the + sign, click your network card and choose delete on top of the window. Reboot and let Windows reinstall it. If for some reason Windows has lost the driver, you'd have to find it elsewhere, either from the Internet with another computer or from the driver disk that came with your motherboard.
2) If that doesn't work, reset Winsock which deals with how Windows handles networking: Again, go to Start->All Programs->Accessories (or type "cmd" in the search bar) and right click Command Prompt (cmd). Left click "run as administrator". You'll get a black window with white text saying "C:\Windows\system32" or something like that. Type "netsh winsock reset catalog" and press Enter. It should tell you that you'd have to reboot for the reset to complete. Close the black window and reboot your computer.
Good luck!
