I'd just like to add that you probably shouldn't be using an insecure protocol like PPTP. With that being said the only other thing I have to say is that you must have configured something incorrectly or don't really know what you are doing. Without specific details(error messages, config files, specific steps) there isn't shit we could tell you except that you did something wrong.
It's a scientific formula really. Ever question yields an equal and opposite response. So if you have a shitty uninformative question, you'll get a shitty uninformative response.
Here I'll start you off. How do you connect to the internet normally?