Is this a mains powered caddy ? or usb powered ?
Reason i ask this,some usb caddies have only 2 usb plugs (red and black) and no mains.Plug both usb plugs into the pc.
If mains powered,the above does not matter.
In My computer,right click the drive/properties/tools and check the drive for bad sectors.
Do you have two internal drives fitted ?
Also check the bios to see if it is recognised.