Cell entries are defaulting to text fields - formulas not evaluating.

[nameless1]

When multiple people handle spreadsheets, things happen. I started with a "normal" (default) XLS and gave it away. When I got this one back, someone had grouped all the tabs, I don't know why, and I had to ungroup them to edit. Now however, one tab in particular always defaults to cells being treated as text. I can reset the format of groups of cells, but I have two problems:
1) I would like to return the default for the entire XLS to be the "normal" default, where you can enter formulas, etc.
2) There are many formulas that appear as text and will not evaluate if the Evaluate Formula fx button is used. Instead, an error appears "The cell being evaluated contains a constant."

Sure, there are ways I could copy and start over, but I would REALLY like know how to restore this worksheet to the normal default behavior, especially as the data is the source of many pivot tables and references that I do not want to update.