Russ my mistake, F12 was the key I pressed when I was seeing if that was what the problem was.
When I was initially trying to MDI I could see nothing wrong and nothing was happening, but I then went to the Diagnostics screen to see if there were any inhibits active on X Y or Z, there weren't but when I tried to MDI from that page I noticed the G Code window was being highlighted, that is when I wondered if it was a Hotkey setup.
I looked and the code window was set to the same key as the Enter key (13 I think), so every time you pressed Enter to use whatever had been typed into MDI it highlighted the Code window thus anything I had typed in MDI was not acted upon. I changed to F12 just to test and sure enough that had been the problem.
Hood