Thanks,muchly,for all your work,mate,but I think I've glitched the game and need to start again.
While I was waiting for advice,I wandered,building exp for crafting.
Now I've gone back,I can get in,I fight the ghouls but the green dragon etc. isn't there and the wall's closed!
I've copied and printed your advice and will use it next time.
Al.
PS I've kept all my saves so if it's fixable I can go back.