Excel date format change

Hello,
I have use MSoffice-2010,in a excel sheet there is some data with 72 rows.Main issue is when I sent the excel sheet to my friend he got the date format is Different in (from 64 to 72 rows),again I sent to another friend he got right format. After my 1st friend uninstall msoffice again install but the issue is same.Some one help me......Thanks