hardisk doesn’t detect in other’s computers

hey……I have a seagate hardisk of 500 gb…….It works fine on my computer……the problem comes when I connect it to someone else’s computer……..it shows the message “the hardisk needs to be formatted”………I cant format the hardisk because I have 400 gb stuff in it……….please give me a solution so that i can repair it from my computer…..pls help