A few points you need to be aware of...
1 - If you are not in Basic permission level mode (default) but using Enhanced, you will not be able to see the items.
2 - The same goes for Basic but you will be able to see the Project and sub items but will not be able to edit them unless you are the Project Manager or Manager.
3 - If the work item is completed, it can no longer be edited. You will need to mark as Active, change and then mark as complete.