For several days I had an .xlsx document without a horizontal scroll
bar. I went to my Excel 2007 advanced settings and that setting was
checked off. I even unchecked it, saved my document, opened it, and
checked that setting. I could move my cursor to a cell and scroll
right.

I finally solved the problem. With my spreadsheet opened, I opened
up another wide, tabbed document (my first document had only one sheet
with data). When I closed that other document, my first one had the
tab and horizontal scroll visible. I closed the spreadsheet and
reopened it and it's working correctly again.

Any idea what caused this problem?

--
"In no part of the constitution is more wisdom to be found,
than in the clause which confides the question of war or peace
to the legislature, and not to the executive department."

- James Madison