Q: i can t open the mail menu on my i phone 3gs

Check Settings>General>Restrictions>Accounts to be sure it's set to Allow Changes.

What mail menu are you trying to open?  The one in Settings>iCoud or somewhere else?

Are you saying that when you tap Settings, then tap iCloud you can't turn Mail to on?  If not, please elaborate because I still can't understand what you are trying to do.

Glad you got it working.