The activation website seems to be active. What do you actually see when you try to access it? You generally should be taken to the NXP website login page - where you can login (if necessary creating an account first).
There is more information on activating LPCXpresso IDE at:
https://community.nxp.com/message/630539
but you also might want to consider using the new MCUXpresso IDE product instead (which does not require activation) :
Regards,
LPCXpresso Support
