NEW INFORMATION ADDED
Make sure the Internet is still working on the downstairs computer. If not reboot the Cable/DSL modem. If you can get on the Internet downstairs then.
Determine if you are using a wire or wireless connection upstairs.
Wireless
1.. Click on View Available Wireless Networks and do a refresh and make sure that the computer can see YOUR router. If it cannot see your connection make sure the wireless is enabled in your computer.
2. Disable then re-enable the wireless connection.
3. Then do the repair option on your connection.
Wired
1. Unplug and replug in the Ethernet cable. On the router make sure the port light for your connection is on. You may want to move it to another port on the router. See if you are getting a link light where the cable is plugged into the computer.
2. On the local area connection disable the connection then re-enable it.
3. Do a repair on the connection.
These steps will usually get you back on the Internet.
Until you get rid of the limited or no connectivity you will not get on the Internet.
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OK Thank you for the added information
1. Insure that your computer is set to obtain an IP address automatically. Go to Start> connect to> show all connections
RIGHT click on the mouse with it over the wireless connection icon. and left click on properties. a local area connection box should open. Double click on Internet Protocal TCP/IP in the
this connection uses the following box. Make sure there is a radio dot in the Obtain an IP address automatically box and a dot in the Obtain DNS server address automatically.
2.Then click on the Advanced tab
Insure the IP address is DHCP enabled.
3. ARE you using a WEP key that needs to be added in the wireless settings. If you are retype in the key.
4 . Do a repair of the connection.
If you still can't get on and it is a laptop. I would take the computer to a WIifi hot spot (probably a local library) and see if it will connect there. If it will then you have a configuration problem between your computer and your router. If it will not then if is probably a bad wireless card or bad built in wireless card. Take it to a computer repair facility or call the computer manufacture.