If your inbound PPTP VPN and Remote Desktop / Terminal Services are failing recently, if you are a Qwest/CenturyLink DSL customer, check the firmware version of your device.
Model Number: PK5000
Firmware Version: QAP002-18.104.22.168.9.9-PK5000
According to the conversation I had with CenturyLink support this evening, a recent firmware update (the version listed above) is breaking PPTP VPN, and in my case, also our inbound TS sessions. CenturyLink is currently working with Actiontec to resolve. The workaround in the interim is to replace the Actiontec with a different model, a Zyxel model using the PK5000z model number.
If you are having trouble, check your DSL modem firmware and then contact CenturyLink support.