|Follow the directions for installing the external drive.|
Some external hard drives have built in backup capability or other hardware or software, built in, and you may need to install the software for the external drive BEFORE you first plug it in.
An external hard drive requires up to the standard maximum amount of current available from a USB port - 500ma - it will not work properly if the USB port you have it plugged into cannot supply enough current.
And/or, rarely, you may have an IRQ sharing problem you need to fix.
See response 3 in this:
A single connection from the external drive to a USB port on it's own cannot supply enough current for the external enclosure's circuits and the hard drive in it. The circuits in the enclosure require only a small amount of current; it's the hard drive itself that requires most of the required current.
External 3.5" drives must have a power adapter connected to the enclosure as well.
External 2.5" drives must be connected to TWO USB ports on the computer end, both of which can supply up to 500ma of current, or one of the cables that has only two wires can be connected to a power adapter with a USB port that can supply at least a minimum of 500ma at 5v, such as a power adapter that can power or charge an MP3 player, or, less commonly, it must be connected to one USB port that can supply up to 500ma and have a power adapter connected to the external case that can supply more than 500ma to the drive.
Recent 2.5" hard drives in external drives often require no more than 1 amp of current at 5v when starting up. Some recent hard drive models, and some older models, may require more current and an external power adapter that can supply more than 500ma to the drive. If you have installed an older 2.5" hard drive in an enclosure, and/or if the newer hard drive you installed requires more than 1 amp when starting up (e.g. some > 200gb), it will probably not work properly in the enclosure unless the enclosure is one that has an external power adapter that can supply more than 500ma to the drive. If the hard drive did not come with the enclosure, look up how much current your model requires on the manufacturer's web site.
3.5" hard drives in external drives require more current than that, total, at 5V and 12v.
If you made connections to the mboard yourself, or some amatuer did that for you,.....
- some mboards (e.g. Asus) that have headers for firewire port connections on the mboard have firewire headers that have an identical number of pins and layout as ones for a pair of USB ports.
If you or they mistakenly connected wiring connectors for a case USB port or ports that are on a plate installed in a slot space at the back of the case to a firewire header, you won't notice any problem until you plug in something into that USB port, but when you do, all sorts of bad things can happen, and the firewire circuits for that header, and the USB device you plugged in, can easily be damaged in a short time, and other mboard circuits may be damaged as well in a short time. If your mboard does have identical headers for a firewire port and a pair of USB ports, you are often warned in the mboard manual to make sure you connect to the proper header.
- the arrangement of pins that are for what on USB headers on mboards for USB ports, and which wires are for what on female connectors for case USB ports or ports on a plate you install in a slot space or ports on a USB device installed in a case bay on the front of the case, etc., was never standardized. If a wiring adapter for ports on a plate you install in a slot space came with the mboard, you can be sure the adapter's wiring connector is wired up right to the USB header, but otherwise, you have to make sure whatever you plug into the USB header is wired up so that it conforms to what each pin in the header is supposed to connect to - see the description of the wiring for the port(s), and the description of the wiring for the header on the mboard.
- some connections for USB ports have five wires for one or both ports - sometimes the purpose of the fifth wire does not conform to what the circuits for the 5th pin in the mboard header expects, and problems will be caused by that - in that case, if you have that problem, you will probably get (an) error message(s) generated by the mboard's bios even when no USB device is plugged into an affected port, once the wiring has been connected to a header, such as something about over current.
If that happens, you must NOT connect the fifth wire from the port, which is either supposed to be for a second or shell or plate ground, or over current, or similar.
On a 5 in a row female wiring connector from a port, the fifth wire usually is on one end and is the same color as the 4th wire, often black. If wires from a port have individual connectors, the color of the 4th and fifth wire is usually the same, often black; if both are for ground, it doesn't matter which you connect to a 4th pin for ground; if one is for over current or similar, don't connect that wire.
If the mboard USB header has 9 pins, 4 in one row, 5 in the other, and which wire is for what is otherwise compatible with the wiring of the pins on the header, and the wiring for two ports has one 5 in a row connector and one 4 in a row, install the 5 in a row connector on the 4 pin side of the header so the 5th wire is not connected, and the 4 in a row connecter on the 5 pin side so the 5th pin is not connected (it being for a second ground, or over current, or similar).