Hello APK100676
When you use Format > Row > Unhide do you have the rows above and below the
hidden row(s) selected?
To highlight from one row to any number of rows below that you simply need to select
a cell in the starting row (or the row number at the left to include the
entire row) and scroll down to the last desired row and hold the Shift button while
selecting the cell (or row number) for the last row.
Also, unless you're using the newest version of Excel you don't have 66,000 +
rows to work with. You'll only have 65,536 rows at best.
If I've misunderstood what you're looking to do then post back with more details.