Suddenly I'm unable to select any object to reposition it. A white circle
with a slash appears when I move over any object, preventing me from
clicking. I've not seen this before. I also noticed the title bar now has
[Group] added to the title of my document. I'm in the dark as to how to
ungroup, undo, ... and how I got here in the first place.

It sounds like your objects may be grouped together, which is why you are unable to select or move them individually. Here's how you can ungroup them:

1. Click on the grouped object to select it.
2. Look for the "Group" button in the "Arrange" section of the "Format" tab. It should be located towards the right side of the ribbon.
3. Click on the "Group" button and select "Ungroup" from the drop-down menu.
4. If the "Ungroup" option is grayed out, it means that the objects are not actually grouped together. In this case, try selecting the object and pressing the "Delete" key to remove it.
5. Once the objects are ungrouped, you should be able to select and move them individually without the white circle with a slash appearing.

As for how you got here in the first place, it's possible that you accidentally grouped the objects together by selecting them all and clicking the "Group" button. Alternatively, if you copied and pasted the objects from another document, they may have been grouped together in that document and carried over to your current one.

If you have more than one sheet selected, you'll see [Group] in the
title bar.
Any changes you make, will affect all the selected sheets.
To ungroup, right-click on one of the selected sheet tabs
Choose Ungroup sheets.

Elementary Computer Lab wrote:
Suddenly I'm unable to select any object to reposition it. A white circle
with a slash appears when I move over any object, preventing me from
clicking. I've not seen this before. I also noticed the title bar now has
[Group] added to the title of my document. I'm in the dark as to how to
ungroup, undo, ... and how I got here in the first place.


--
Debra Dalgleish
Contextures
http://www.contextures.com/tiptech.html