Photoshop and PSE have a handy feature that makes it easy to edit type. With the Text Tool selected, the software detects when you move the cursor close to existing type. Photoshop and PSE are programmed to assume that you want to edit your type, so the software selects the existing type layer. This is helpful most of the time, but if you are trying to add new text close to your existing type, this feature prevents you from being able to perform the task.
When this happens, you can disable the feature by holding the Shift key as you click with the Text Tool. Holding the Shift key allows you to create a new text layer, ignoring the existing type. You can even create a new line of text on top of your existing text this way!