WD Passport is no longer recognised by my mac

I have a 5 week old WD 320GB Passport that has been working fine and now all of a sudden when i plug it in to my Mac Book Pro a box pops up saying this hard drive is not readable and do i want to initialize it, ignore or eject. i am about to have a photography exibition with images stored on this drive that have not yet been back up anywhere else so I can’t initialise the disk as i will lose my work - what can I do to recover my images…?