When you connect to VPN using PPTP connection on Windows it is possible to encounter problems caused by DNS. The result is that some services or sites are not reachable.
The behavior is caused by the fact that Windows is using your ISP’s DNS (resolving name servers) instead of the DNS provided by the VPN service. The issue is a well know problem of the Windows operating systems.
More information about this you can find here.
The solution is to perform a little trick in the registry (via Microsoft Help and Support):
1. Click Start, click Run, type regedit32 in the Open box, and then click OK.
2. Click the following registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Linkage
3. In the right pane, double-click Bind.
4. In the Value data box, select the “\Device\NdisWanIp” item, press CTRL+X, click the top of the list of devices, and then press CTRL+V.
5. Click OK, and then quit Registry Editor.
If you are not familiar with the Registry Editor you should download the following Visual Basic script, save it on your computer (anywhere you like) and run it (just double click on the file). It performs the actions described above.
Important! Every time a new VPN connection is created, a DNS change is performed, an new IP address is allocated, the registry settings will be overwritten and the problem will be present. In this case, you should follow again the steps described in the solution.