why does my apple tv keep asking me to authorize the computer when it is already authorized?

Hi All, I'd be grateful for your help. Setting up my Apple TV (current generation) was no problem. However, if my modem and wireless router ever reset (which happens quite often as we're currently in Indonesia), things go all hay-wire. I have no idea how to reconnect Apple TV properly. It seems to see my computer, and still seems to know all the content, but if I try to play anything it asks me to authorize my computer. But it's already authorized! I've tried de-authorizing and re-authorizing. I've tried restarting Apple TV, restarting the modem. How to fix this easily? Argh!

Thanks,

Amit