It was fine last night, and when I looked at it this morning the screen has gone all funny with thick black lines in it. I have re-booted it several times but no change 
It is actually 4.6 yrs old so I guess it has done quite well really.
So I guess I am going to bite the bullet and purchase another one 
I spoke to customer services and the best they have offered is a refurbished one for £45 (the cheapest version).
So which one do I go for? I don't want one where the screen lights up too much (fire?) as it hurts my eyes (have kindle app on iPad).