serial ATA drive as USB hard drive help

[gavgravity]

Just removed my old Maxtor serial ATA hard drive from my dead Imac and tried connecting via a USB adaptor to retrieve all the data.
All connected simply but is not showing up as a USB devise- drive?
Does anyone have any experience connecting in this way? thanks for any help

 

[spinnerlys]

Where does the drive get power from?

It's a 3.5" drive, isn't it?