My gateway laptop suddenly stopped letting me type. The keyboard is locked. When I type a letter it says, "this modification is not allowed because the selection is locked."

Are you using word 2007 and this is happening?

If so, here is some info - either a setting or your trial version has expired
Microsoft Word: "This modification is not allowed because the selection is locked." - 404 Tech Support (http://www.404techsupport.com/2009/01/13/microsoft-word-this-modification-is-not-allowed-because-the-selection-is-locked/)