send button is dimmed, not blue, cannot send message

Check

Settings > Message > iMessage and make sure that is on

Also check

Settings > Message > iMessage > Send and Receive and make sure that your mobile number, iCloud email address and email address are there

If after doing all this, it still does not work, try a reset,

Reset your iPad by pressing the 'Sleep' and 'Home' button at the same time for about 15 seconds or so. Your iPad will then go through a reset / reboot procedure and will be ready for use within about a minute.

Don't worry about doing this as you will not lose data or settings.

Good luck and do report back.

Make sure receiving party have enabled iMessage.