Sorry, to be more specific - I assume you are using one of the CS versions of Photoshop. For each tool, there is a horizontal toolbar just under the main File-Edit... menubar. For the crop tool, there are small windows for Width, Height, Resolution, and some other buttons. If the windows have values in them they will modify your selection. Using the 'Clear' button (as others have noted) should erase any entries and let you select freely. I didn't have Photoshop open and used "normal" instead of "Clear" to set things back to the default operations. If this doesn't work, you can try using the selection rectangle (just above the crop tool in the tools window) and selecting "crop" from the Image menu.