What to do when haven't heard back from potential supervisor who is moving? I had contacted a potential supervisor and got a positive response from him. He said that he is interested but he said we should do a skype interview first. He also stated that he is moving to another university in 4 weeks and explained a few conditions and asked if I am still interested. I had no issue with the place or university since I am interested to work with him so I replied and sent my skype id for interview. Its been a week and I haven't heard back from him. I think he might be busy as he said that he will be moving to some other university. 

Shall I write him again and if yes how do I start the conversation again or shall I wait for his response?.
I cannot agree with Neo: one month is awful long time in any conversation, and I would take that long wait only if explicitly said to contact months later. Long time is a problem because 1) he forgets what was it about, 2) it can give the impression that OP is maybe not that enthusiastic about the opportunity, 3) in a month a lot of things can happen with an open position.... 

People can forget mails, or not answer even if they not forget them, especially if he is busy and not you are his first priority. Just send him a polite follow up email: remind him in the first sentence or two about your discussion and he was positive about you. Then ask about the Skype interview, how you can roll this etc. 

If you are afraid that he is busy and you are too pushy, you can just state that you know he is busy so if he wants to postpone this conversation / scheduling the interview after his move, you are totally fine (are you? do you have any deadlines to care for?). If this latter happens, still ask that you will follow him up a month etc. later, if it is good for him. Busy people dont like to be pushed in a schedule, but if no one sets expectations for a schedule (any schedule that convenient for him), nothing will be done and also kind of unprofessional.

(I assume this story is about US. Different countries call for different level pushiness.)