What happens when you command click on the T icon in the layer thumbnail? (CTRL click if on Win). If you get marching ants, you may have a layer blending mode may not be set to normal or your opacity or fill is set to 0%.
If you do not get any marching ants, you may have set your type inside a really small text box and it is overflowing. Try changing the font, incase you have a font with a strange descender height or a technical problem with aht font.
The box I have the text in appears, but there are no marching ants and my text is small enough (size 14) and the box is large enough it should not be overflowing, but I went ahead and really enlarged it and still nothing. I've even tried simply highlighting the text and I can't, no highlight will even appears.
You might try a screen shot and use the camera icon above to upload. Include all the pertant parts so we can see what you see.
If your colour and blend modes are sensible, then it is usually a size issue. Text size defaults to Points, which is OK if you are in the print industry, but it has always made more sense to me to set text size in MM or inches.
This way, regardless of the resolution set in image size, if the image is 10 x 8 inches, and you set type to 2 inches, you know you can expect the type to be 1/4 of the document height.