Galaxy S4 mini - keyboard/password problem

[Dandeleo]

I've suddenly started getting a "sign in with your Samsung account to continue using Samsung services" screen which blocks me from doing anything else until I put in the password. The trouble is, I can't put the password in because the keyboard wont activate when I tap in the box. my only options are "cancel" which circles back to the same point, or "forgotten your id or password" which I tried in desperation, changed the password on my computer, and then the phone still wouldn't allow me to enter it.

Turning the phone off, removing the sim and replacing it, this gives me a minute of unlocked phone use and then the screen comes up again. WTF?

help!

 

[chanchan05]

What keyboard are you using? Are you using the default samsung keyboard?

 

[Dandeleo]

What keyboard are you using? Are you using the default samsung keyboard?

just the usual on screen keyboard that's supposed to come up when you tap the password box - nothing additional. occasionally after madly tapping it I sometimes get it to come up but I can only get a couple of letters out before it vanishes again.
Last week I did have a warning that i was using a lot of memory so I deleted some photos. I don't have much in the way of additional apps and no extra games. could this be related?