At some point in time, opening a cube left the cube viewer window off the screen(s)-had to use windows and left, right etc. to bring into view.
Found a TM1P.INI located in C:\Windows - removed this whilst not using any TM1 client components. All good now.
Edit: Removing the TM1P.Ini in the %appdata% folder did not work, nor did the one in ProgramData...
@ADMINS - please move this to Tips&Tricks as I cannot post directly. Thanks.