iPad Air & iPhone 5 w IOS8 suddenly won't text (iMessage BAD) send is gray or Red? After I had to change my email associated with my Apple ID, both my iPad &amp; iPhone have gone berserk. Both are iOS 8. I have already repeatedly:  

Rebooted, signed out, clean the cache, reset all settings, reset the network (which gave me the added problem of now seeing "No Service" displayed in the upper left corner despite having service) erased all messages, rebooting each time I did anything.  I'm now reaching you on a totally ERASED &amp; set up as new iPad... That still doesn't text!

Especially on the iPad, now, even after totally erasing and resetting, I go to Messages
Type in a name of a friend who DOES have an iPhone 
The name is coming up in RED?

If I type in the message area, (back when the names were NOT RED) the SEND button was GRAYED OUT   you could not send 

OR 

And this was the first problem... I would compose a text, with or without a photo no difference. ... Phone or iPad, and get a red ❗️ With the notation 'message not sent'

It does not matter if the person has an iPhone or not.  The iPhone might send a plain text but no longer will send photos.  

I tried to match settings from iPhone to iPad, but that didn't help. (The iPad doesn't use cellular, btw). The iPhone apparently will still allow SMS messages, but the iPad will not.  If I turn off that option and try to text, a sign in comes up and puts it back to iMessage. 

I am nowhere near a "genius", and the two hour drive to them once was totally unsatisfactory.  Siri found this site for me.  I have my fingers crossed.
You said you had to change your Apple ID email associated with your account. I just want to make sure you signed out of the old one and signed in with the new email address under "Settings > Messages > Send &amp; Receive" on both devices. After you do this, uncheck Settings > Messages > iMessage, wait 15 minutes and check it again.