external hard drive not seen in disk utility but can be seen in system profiler

HI

i have a 500gb western digital my passport, its been working fine, since i have used it on a windows machine, i can no longer get it to be recognised in finder. The light is flashing on the side and i can see it under USB in sytem profiler. I cant see it in disk utility. i cant format as it has photos etc loaded

cheers