WD My Passport Essential 500GB is not being recognized any more

I have huge problem. Up to this day everything worked fine, but today I connected WD to my Mac and it was not recognized (checked in Disk Utility and also there was nothing), connected to Vista and Windows 7 and also the same, (no signs of drive in Devices Management) I tried changing USB cable but still nothing. However the white light is flashing constantly on the edge of the drive. Tried to reboot computers, to disconect, connect everything and also nothing, do you have any tips what's going on?