base 1 again?

I got 2 of my handsets working with this but one died a week later (I kinda knew it was on it's way out poor thing).
Bought 2 replacements 2nd hand off the bay of e.
They weren't ringing in sync with each other and caller display not working, so I de-registered them all and re- registered.
Now just got 1 that is just flashing base 1 and tried unplugging base & holding green call button down several times but not working ........ help please.