ADE is unfortunately a very poorly designed and coded program.
I don't know why it lost your activation.
Probably it has only half lost it, which is why it doesn't respond when you try to reactivate.
Try using ctrl-shift-D while running ADE (cmd-shift-D if on a Mac); that should completely remove the old broken activation (even reinstalling doesn't do that).
Restart ADE and try to activate again.