Try reinstalling the WAN Miniport (PPTP) driver.
1. type device manager into the start menu and open it
2. then select "Show Hidden Devices" under the View menu.
3. Expand Network adapters. You should see the WAN Miniport (PPTP)
4. right-click and select uninstall then reboot.
It should automatically reinstall the driver after the reboot, let me know how it works.