I've bought an external 3TB Toshiba hard drive without casing that we're putting in a caddy and attaching to our PCs. But it's not mounting. It does mount on a Macbook Pro. All our PCs are Windows XP SP 3. Is this the problem and is there a solution?
It could simply be that Windows is not assigning a drive letter to it when you plug it in.
Go into Disk Management.
In the bottom-right panel, find the ribbon which relates to that device (it usually says "Raw" with no device name).
Right-click that and choose "Change Drive Letter and Paths".
Click "Add" then choose a letter or accept the default letter.
Click 'Next' or 'OK' and wait a few seconds for it to update itself.
But it does't even show up in disc management. The computer makes the noise to show that something has been plugged into the USB socket and I can eject it from the eject disc symbol in the bottom right hand corner but it has no drive letter in that, and, doesn't appear in My Computer or disc management.