Pipedream, it sounds like a font problem. Go under "Window" and click "Character" if that palette isn't already showing. When you have the text tool selected, what does the Font field in the Character palette say? At what size is your text set?
Also, the type tool will usually create a new layer on top of all the others. But maybe it's under another layer for some reason, rendering what you type invisible for the moment. Let me know if any of this helps.