This has plagued me for ages and I FINALLY figured out why it happens. I have not seen this explained anywhere online. It has affected me since CS2, and I’m using CS5 now. Other versions are probably also affected.
You may have already found that you can fix this problem by pressing the button to Clear the Crop tool preferences. But it doesn’t always stay fixed. Somehow it keeps putting a 1 in one of the Crop Tool dimension preferences. You go to make your crop and. . . the image is gone, reduced to 1 invisible pixel onscreen.
WHY!??!!? Adobe why u do dis?
You’re doing it to yourself. I just got a new keyboard and it has an enter key where I sometimes hit it by accident. Not a Return key like you normally have over the Shift key. An ENTER key, like you find on the tenkey area on your keyboard. These are not the same. Striking the Enter key puts a zero in the Crop Tool preferences, which is an invalid entry. It doesn’t do whatever you were wanting to do when you hit Enter by accident. The usual action to take when Photoshop messes up somehow is to hit Escape to make it exit whatever it was doing. Hitting escape after putting a zero in the crop tool dimensions tells photoshop “whatever dude, just figure out what size I wanted to crop my image”.
Hitting escape changes the zero to the next-valid number: 1
Then you hit your image with a crop, and Photoshop faithfully crops to one pixel, just like you told it to do. Instead of a ragequit, hit Clear again, and try to avoid striking the Enter key, or any keystroke combination that adds up to Enter on your keyboard.
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