Unable to access a map of the galaxy. Therefore can't navigate Normandy

'X' key?  'A' key?  Are you trying to play with a game controller?

No, using those keys was advice on a ME on PC forum. 

Using a standard k/b & mouse. 

Also, spacebar doesn't work either. F6 will do a fast save & (as I say above) 'O' opens the codex. No other key on my k/b has a response. (I've tried them all). 

This is whilst standing at the top of the ramp, against the railing, facing forward, backwards, sideways & everything else I could think of. 

The default interact key on PC is E. Normally you should be able to see an interact icon on the galaxy map when you're standing close to it. It's the same as opening doors or talking to people.

The advice to press A or X was almost definitely in reference to consoles, because those are the interact buttons for Xbox and PlayStation respectively.