and if that fails, things get more complicated...
Step #1
Full uninstall of TCP/IP.
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These steps are copied from
http://support.microsoft.com/kb/32535611. Locate the Nettcpip.inf file in %winroot%\inf, and then open the file in Notepad.
12. Locate the [TCPIP.PrimaryInstall] section.
13. Edit the Characteristics = 0xa0 entry and replace 0xa0 with 0x80.
14. Save the file, and then exit Notepad.
15. In Control Panel, double-click Network Connections, right-click Local Area Connection, and then select Properties.
16. On the General tab, click Install, select Protocol, and then click Add.
17. In the Select Network Protocols window, click Have Disk.
18. In the Copy manufacturer's files from: text box, type c:\windows\inf, and then click OK.
19. Select Internet Protocol (TCP/IP), and then click OK.
Note This step will return you to the Local Area Connection Properties screen, but now the Uninstall button is available.
20. Select Internet Protocol (TCP/IP), click Uninstall, and then click Yes.
RESTART
For good measure you should delete the following keys before reinstalling TCP/IP in step #2 (go into regedit from start > run to do this)
HKLM/system/CurrentControlSet/services/winsock
HKLM/system/CurrentControlSet/services/winsock2
Step #2
Reinstall of TCP/IP
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Following the above steps from 11-13, replace the 0x80 back to 0xa0, this will eliminate the related "unsigned driver" error that was encountered during the uninstallation phase.
Return to "local area connection"> properties > general tab > install > Protocol > TCP/IP
You may receive an "Extended Error" failure upon trying to reinstall the TCP/IP, this is related to the installer sub-system conflicting with the security database status.
to check the integrity of the security database
esentutl /g c:\windows\security\Database\secedit.sdb
There may be a message saying database is out of date
first try the recovery option (in a command prompt window)
esentutl /r c:\windows\security\Database\secedit.sdb
if there are any problems, use the repair option (in a command prompt window)
esentutl /p c:\windows\security\Database\secedit.sdb
rerun "esentutl /g c:\windows\security\Database\secedit.sdb" to ensure that integrity is good and database is up to date.
Now return to the "local area network setup"
choose install > protocol > tcp/ip and try again
Reboot
Pray