Do you have any kind of 3rd party Network Manager installed, like Bonjour, Netmagic, and the likes?
Do you have any "Fancy" 3rd party security suits, or Firewall like the nVidia hybrid Firewall.
Are you using more than one Firewall (including Windows Native), AV, or other active security applications?
If you do use any of the above, try to get rid of them and see if it helps (
Get Rid, means Get Rid, Not just Disable ).
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First scan the computer for Viruses and Malwares.
When you are sure that it is clean.
Check the Device Manager for valid Wire card entry.
http://www.ezlan.net/Win7/net_dm.jpg
If there is No valid entry, delete any Bogus Entry, and re-install the Wire card's Drivers.
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Try to install the latest drivers of the card from the support page of the manufacturer.
Download the drivers and unpack them to a folder of your choice.
In the Device manger, right click on the adapter.
Click on Update Drivers, and choose the Browse my computer for drivers,
Choose let me pick from a list, Click on Have a Disk and point to the folder with the Drivers.
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Check the Network connections to make sure that you have a Local Area Connection Icon/Entry, and that the Properties of the Icon (right click on the Icon) are correctly configured with TCP/IPv4 protocol in the Network Connections Properties.
http://www.ezlan.net/Win7/net_connection_tcp.jpg
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Make sure that No Firewall is preventing/blocking the Wireless components to get to the Network.
Some 3rd party Software Firewalls/AV/Security suit,s keep blocking aspects of Local Traffic even it they are turned Off (disabled).
If possible configure the Firewall /Security suit correctly, otherwise totally uninstall it, and get rid of its residual processes to allow clean flow of local network traffic.
If the 3rd party software is uninstalled or disables, make sure that Windows native Firewall is On .
3rd party Network mangers like Bonjour, NetMagic, and others can block local traffic too.
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Log to the Router's menu from a working computer and make sure that the DHCP is On and it is configured to assign IPs that can cover the number of computer that are connected (few more will be even better).
Switch Off the computer and the Router, Reboot the Router, and the computer.
Right click on the Wire card Network Connection, choose Status, Details, and see if it got an IP and the rest of the settings.
On IP status.
TCP/IP and its variables typically look like this.
Right click on the Wire card Network Connection, choose Status, Details, and see if it got an IP and the rest of the settings.
Typical TCP/IP status looks like this.
http://www.ezlan.net/Win7/status-nic.jpg
Description is the card manufacturing data.
Physical address is the card's MAC number.
The xx should be a number from 0 to 255 (all xx same number).
yy should be from 0 to 255
zz should be from 0 to 255 (all zz the same number.
The lease date should be valid to the current time.
*Note 1. IP that starts with 169.xxx.xxx.xxx is not valid functional IP.
*Note 2. There might be an IPv6 entries too. However, they are not functional for Internet traffic or LAN. They are needed for Win 7 special HomeGroup configuration.