The Crop tool is missing the "accept" icon at startup if W & H have been specified previously and image has aspect ratio of other than WxH.
To reproduce, load any image, press "C" to select crop tool, then specify W and H as 8in and 10in. Close the image, then open any image that has an aspect ratio of other than 8x10. Press "C" to select crop tool. The "accept" icon is missing and you can't approve the crop shown on screen.