Hello, is this resolved? If not, may I suggest two things? I frequently must activate and re-activate windows 8.1 because of hardware changes or imagining install on a different computer.
If it isn't resolved, the next time it says you need to activate, try to activate through the microsoft telephone system. The computer should bring you to the area where that telephone number is located along with the areas to place the numbers the automation telephone line gives to you. If you can get through all that you should have that nag issue stopped.
If you can't get that far in the telephone automatic registering within the computer you have, then I suggest calling microft support. Gather up all of the product ID and or keys for windows 8.1 that you have before you call. If its' within the first 3 months of the initial activation then it is still under warranty for free support and they will do whatever is necessary to get you all whole with that program and its activation.-free.
If it is after the 3 month initial activation then it's a bit more difficult to get it done free, but still they do all they can to help you wih it.
I just want to put in a good word on their support there because one time I got into a situation where I was being transferred all over the world from the (extension department) they call 8.1 to the technical department and back. Seven times. Finally I asked for a superviser and he stopped the confusion right there and thankfully had the authority to order me a fresh new disk (normally costing over $100.00 retail). Free. So, they really do all they can to get you legally registered, but if all else fails, ask for a supervisor early on. Good day. Rob