Hide/Unhide Rows or Columns:

To hide/unhide a row(s):
To hide a row(s), select a cell(s) and press Ctrl+9.
To unhide a row(s), select the cells containing the range of the hidden row(s) and press Ctrl+Shift+(.
To hide/unhide a column(s):
To hide a column(s), select a cell(s) and press Ctrl+0.
To unhide a column(s), select the cells containing the range of the hidden column(s) and press Ctrl+Shift+).
To unhide rows & columns in a sheet:
1. Press Ctrl+A to select all cells in the sheet (in Excel 2003, press Ctrl+A+A from a cell in the Current Region/List range) or click Select All at the top-left intersection of the rows and columns.
2. Press Ctrl+Shift+( and then Ctrl+Shift+).