First try resetting the type tool from the drop-down menu.
If that doesn’t help, try resetting your preferences as described in the FAQ.
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You either have to physically delete (or rename) the preference files or, if using the Alt, Ctrl, and Shift method, be sure that you get a confirmation dialog.
This resets all settings in Photoshop to factory defaults.
If the problem is still there, start looking for a bad font.