Re: no user_activation_key inserted
couple of thoughts –
Is your base WP install working correctly – does it send admin emails notification correctly (e.g. when a new user is added in WP backend)? If not, it is a base email configuration problem.
Have you got any additional plugins installed – one of our clients had a problem with a CAPTCHA plugin interfering with the activation process.
If neither of these, there are a number of threads on this site, dealign with the problem of activation emails not being sent – it might be worth searching those.