Ok, so I have tracked down what may be the issue with the ethernet connection. It may have to do with the boot up process.
If the SD card is not in, BBB won't boot up at all so it is booting from the SD card.
If I power the BBB and putty into it using the USB I get :
Debian GNU/Linux 8 beaglebone ttyGS0
BeagleBoard.org Debian Image 2016-06-19
default username:password is [debian:temppwd]
beaglebone login:
I can then apply the 5v (so I don't lose power) and ssh into it via ethernet and I get:
login as:
Notice I don't get the Debian GNU/Linux . . . . until after I log in but I can then keep working.(this may not be important)
As soon as I power everything down it is like it forgets that it can connect via ethernet.
So what I have been doing is to putty to BBB via USB connect the 5V power supply so that I don't lose power when I disconnect the USB and then putty via ethernet.
It's a clunky way to do it. There's got to be a way to force it to remember . . .