Often this is due to the new connection dialog being off screen (usually due to changing monitor setup e.g. 1 to 2 monitors or resolution change etc).
If so the really easy fix (if your connection dialog just needed approval without changing fields) is :
- Focus on SSMS and Hit Enter/Return
..or the easy fix (if above does not work – as your last connection is not ready to go) is:
- Alt Tab to SSMS
- Alt + Space – context menu
- M – select Move (in offscreen context menu)
- Arrow Key(s) – to move it back onto screen
As per answers here from @Eirik Toft and here from @Lee Chetwynd