I bought one, and I've plugged it in, with both USB ports, and nothing. Doesn't appear. Is there something I need to do first? When I plug in a flash drive it works fine

If the drive itself is not formatted then it will not show up in My Computer. Look in Disk Management for it. Is the external AC powered? If so you need to connect the power cord to the AC.

thankyou very much. sorted

Common USB problems

- some devices do not work properly when connected to a USB hub, that is, a hub that is two or more ports connected to one USB port directly connected to the mboard, even if it is a "powered" hub that has an extra power supply so all the ports can be supplied with the standard 500ma even if all ports have something in them. If that kind of hub is not "powered" it shares the 500ma the one directly connected port provides with all the ports in the hub, and that can cause problems when more than one device is connected to the hub. Most multiple USB ports higher up on a case front, USB ports on a keyboard, and USB ports on a printer or all in one are this latter type of hub.
- some wiring to USB ports on the front of a case, usually the two lower down on the case, that is wired to two port connections on a USB mboard header, is inadequate and some devices will not work properly plugged into those ports.
e.g. such front ports I have on one case work fine with mice and keyboards (USB 1.x devices) but will not work properly with USB flash drives, printers, scanners, or an iPod Shuffle.
- ports directly connected to the mboard, or ports in a USB controller card in a slot, or ports in adapter plates at the end of slots that connect to individual ports on USB headers on the mboard, are the most reliable ports to use.
- Check the current voltages in your bios Setup. +5v should be within 10% of it's nominal value. If it's too high or too low, and/or if that or +3.3v or +12v are not within 10% of their nominal values, replace the power supply as soon as you can - it's failing.
.........

Less common.
An IRQ sharing probem.

- If any of the USB controller related devices share an IRQ with another device other than another USB controller related device, that can cause weird problems, especially when a more sophisticated USB device such as a printer or scanner or modem or sound adapter or network adapter is also connected.
Look in System Information on the left side - Hardware Resources - IRQs and see if another device is sharing an IRQ with a USB controller related device.
It's OK for several USB controller related devices to share the same IRQ, and for USB controller card related devices in a slot to share an IRQ with onboard USB controller related devices, and for USB controller related devices to share an IRQ with other devices built into the mboard.

If it's card other than that that's sharing an IRQ, try moving the offending card to another slot - don't use the last PCI slot on the end closest to the middle of the mboard for anything except a PCI video card - that slot is forced to share it's IRQ with the video and that usually causes problems.
......

If a device was sharing an IRQ with USB controller related device, after you have cured that problem you must re-load the Windows USB stack.

Open Device Manager.
Un-install the USB root hub(s) and host controller(s) *in that order*.
Unplug all USB devices.

If your keyboard is USB, hold the power button in until the computer shuts off.

Plug in your USB devices, or at least your usb mouse and usb keyboard if applicable.
Boot the computer.
CHKDSK may want to run while booting - let it.
Windows will automatically reload the USB stack.
Try your USB devices.
..

If your keyboard is PS/2....

Shut down the computer.
If you have no mouse with all USB devices disconnected.....
Hold down Ctrl and Alt, press Del, let go of the keys.
Hold down ALT, press U, let go of the keys.
Press U.

Plug in your USB devices, or at least your usb mouse if applicable.
Boot the computer.
Windows will automatically reload the USB stack.
Try your USB devices.