"Block" meaning what exactly? Hiding them...if so, in VBA:
Rows("10:20").hidden = True
or simply hide them. Then protect the sheet.
Or, format them as Locked and protect the sheet if "block" means unable to enter data in rows but still keep them visible.
Worksheets also have a ScrollArea property to keep certain ranges from being selected but stay visible.
Or maybe you mean something else, so some details from you will help others you get an answer you can use.