I can’t activate an IPad that I have not used fir some time

While this says for iPhone the process is the same for iPad if you see the activation server is temporarily unavailable: If you can't activate your iPhone - Apple Support

What do you mean that you can “unlock it”?

If you unlocked it, it should be working.

What, exactly, has happened with that iPad?

If it is unlocked, where is it stuck at and why can you not get any farther?

More info, please?