External Hard Drives Not Recognized


I am working for someone in India who has two USB 2 external hard drive devices that he uses with PCs (both share the same generic brand and were perchased here). When plugged into either of my two USB ports, the drives won\'t mount on my PowerbookG4. I have had no previous problems with external devices such as a mouse, keyboard, printers, or cameras that were all used with these PCs. The hard drives have been reformatted to NTFS and FAT32, but with no luck. The green light is lit on the actual hard drive device when plugged into my USB ports. Both drives are completely unrecognized my Powerbook, though the same drives were previously used and recognized by a former employee\'s older IBook. Any advice would be great.
which os are you running?
i.e is the external hd recognised by disk utility and can you mount it this way ?