wrote: It won't always register as a new device.
Correct it won't.
If you have all your four slots which is the maximum allowed number of devices filled the app cannot register as a new device. What you need to do is remove a device (the one you used to use Sky Go on that required Silverlight). Yes REMOVE the device. This done on the Sky site by logging on, going to Manage and manage my devices. Then call Sky on 03442 414141. Tell the nice person you speak to that you have been forced to remove a device as the result of being required to download and install the NEW Sky Go App. The reason you need to call Sky is because if you have reached your maximum number of four registered devices you can only make one change per month. Removing a device is a change (I know, stupid right!) and you will get a notice informing you that you must wait a month for a new slot to become available! The nice person at Sky will arrange for a new slot. In my case it took about 20 minutes for the slot to become available. Then you open and use the new Sky Go App which will automatically register your PC as a new device and Robert becomes your fathers brother. Simples. Actually no it's stupid and very frustrating but it's the only way to do it. This isn't an issue on IOS devices because the didn't use Silverlight.
This is how I managed it yesterday after lots of help from others. Hope this helps. Good luck.