Double-clicking the actual text object (is that what you are asking) has no effect. If I select the layer in the layers palette, and then select the text tool, I click on the text and it creates a new text layer. The layers are not locked, so I do not know what is going on. Been a PS user since CS3, and this has never happened before.
When you move your Type tool, look closely at the cursor. If there are dotted lines around it, that indicates that you are about to create a new text layer when you click. If there are no dotted lines, you are about to click inside existing text. It you want to edit text, either click in the middle — don’t get too close to the edge — or use the layers panel and double-click the T in the thumbnail area.