Sorry to bring this up again, but it seems my validate is there sometimes, and sometimes it isn't. I've uploaded a screenshot showing the "isn't" view - I didn't change anything at all.
http://technomom.com/sigilnoval.jpg
When this is the case, Ctrl + Shift + V does nothing at all.
I did a little testing, and it seems to happen when I launch Sigil by clicking on a file. If I use the start menu shortcut, I get the validate option, but I lose some of my menus, like Format and Tools.
http://technomom.com/sigilnotools.jpg
I'm running version 5.3 on a 64-bit version of Windows Home Premium.
Thank you!