How can protecting the sheet delete the sheet??


This is right out of the help file in excel....

Specify which cells can be changed after a worksheet is protected
To unlock cells so that they can be changed, the worksheet must not be protected. For information about removing protection from a worksheet, click .

Select the cell range you want to unlock.
How?


On the Format menu, click Cells, and then click the Protection tab.


Clear the Locked check box.
Note After you protect the worksheet, the cells that you unlocked in this procedure are the only cells that can be changed.

Tip To move between unlocked cells on a protected worksheet, click an unlocked cell, and then press TAB.