If you want to deactivate TCP/IPv6 completely in the following operating systems: Windows 7, Windows Server 2008, and Windows Server 2008 R2, then it's not enough to uncheck Internet Protocol Version 6 (TCP/IPv6) in your network card properties. This tip will help you disable it completely, just follow the given steps.
1. Open Windows registry editor by pressing Windows + R keys, type regedit, then press Enter.
2. Navigate now to this registry key using the tree menu:
HKEY_LOCAL_MACHINE >> SYSTEM >> CurrentControlSet >> Services >> Tcpip6 >> Parameters
3. On the right side of the window, make a right click, then select New >> DWORD (32-bit) Value.
4. Rename this latter as DisabledComponents, double-click on it, then give it ff as Hexadecimal value.
Restart now your system so that new changes take effect. If you want to enable again TCP/IPv6, then delete DisabledComponents key or set its value to 0.