Reason why the harddisk not working in enclosure

Stupid me for making such a stupid mistake: I was a bit fustrated for an hour wondering why a 60Gb harddisk that I taken from my desktop was not working in my Firewire/USB1.1 harddisk enclosure. Finally I figured out a very simple reason: the harddisk was in Slave mode due to the jumper setting. Once I reseted the jumper to the proper master mode, the harddisk worked like a charm. How stupid I was.