Once you change the name from Title to something else, you are stuck - you can never call it Title again since it is a reserved name by SharPoint.
Rename the Title to "Item" or "Item Title" instead - this is usually a suitable fix (I've been through this a few times when my Content Editors go a little nuts)
Once you have the Content Type working with a better generic title field, like "Item" you can go into each of the lists and change the Title field to something more useful locally (NOT in the content types). For instance in a Contacts list - the title would probably be "Last Name" - or in a custom product list the title could be "Product"