Well I can report the problem has gone.
I was doing some work on the laptop whilst just running on battery and the pc asked for a restart I clicked on ok and strangely enough it completed the restart without intervention. (all the previous problems had been whilst running on mains)
To test the theory I hooked up to the mains booted up and clicked restart from the start menu and sure enough it failed to restart.
now (if you bear with me

) when on battery I had no usb stuff attached (hub with thumb drives + wirleless mouse) so I left these unattached and booted up on mains and it completed a restart....yeah.
So I connect my D-link 7-port usb hub and restarted again and all was fine, then reconnected a usb external drive and again all ok.
The problem was with the wireless mouse, as soon as I attached the usb dongle the problem reappeared.
I eneded up swapping the wirelss dongle to a port on the pc and the external drive to a port on the hub.
don't ask me about the science behind this

, but the laptop now restarts ok both on battery power and mains power.
Thanks for eveyones input on this. much appreciated.