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Do you mean you wanted to protect the whole spreadsheet or just the hyperlink?
If you are talking about protecting the whole spreadsheet, then go to review tab and click on protect sheet or protect workbook. That way no one can change anything on your spreadsheet.
As far as getting your hyperlink working again, go to review then click on protecting the sheetthen go down to "Insert Hyperlink" option and make sure it has a check mark by it.