Excel shortcuts

Hi, some excel and powerpoint keyboard shortcuts seem to have stopped working and I am guessing that I've accidentally changed a setting somewhere but I don't know which setting and where to find it.

As an example, in excel the shortcut 'shift + space' selects the row and this works fine. The related shortcut 'control + space' USED TO select the column however stopped working one day and there is now no action that happens.

So far as I can tell all of the other shortcuts that I typically use e.g. 'control + u' to edit a cell, 'control + command + v' for paste special etc continue to work as they always have.

What have I done!!!!?