if you are using a laptop, maybe you will have to configure catalyst to use the right graphic card (the radeon one) with the game executable. I had to do it with a nvidia one
hmm now u mention is samething happened to me.. it asked to me to activate it again when i upgraded the video card recently. And i'm pretty sure it asked to me to activate it ~3-4 times total so far.. not sure why it asked me to activate it first 2-3 times cos it was while ago.
Anyway how many times can you activate it in total? and can you check how many times your account has been activated?