ok I've had a nightmare but seem sorted now.
I didn't have a back up so lesson now learnt.
I tried a couple of suggestions already posted, rebooting, cmd r and wireless issue this did not resolve. Cmd L did not work.
after several reboots I did eventually get in with Yosemite loaded. All seemed ok but on next reboot it started to load again and got stuck. It remained so overnight.
read a few more posts on different sites. Noted MacAfee was a potential issue. So went in via safe mode holding shift, cleared a couple if start items as suggested in the post above and also removed MacAfee.
I have since restarted a couple of times without issue. Not sure exactly what fixed it but doing a combination of previous advised posts I git there.
off to buy a hard drive to do full back up.