Let's start over! What version of Visio are you using? I am only familiar with up to version 2010....and, now that I am retired, I only have version 2003 installed (so that is all that I can work with).

I am not familiar with the "Geometry box" as you call it but, I work with Toolbars. If you click on the VIEW ribbon and click on TOOLBARS, then DRAWING, you will find the various lines you can work with...one of which is the ARC (or, curved) line. Once you click on the ARC and start your line drawing you should be okay. If this does not work, you have other problems. I am guessing that you may have to re-install your software.