Problems with Tape Drives or other Mass Storage Devices

My external mass storage device does not appear to switch on properly.

First Step : Check it is receiving the correct power through the power cable.
More information : Make sure the device is plugged into a wall socket that is supplying the correct voltage. Try plugging something else into the same socket to make sure. If you have a socket tester, make sure that the voltage is steady and at the correct level. (240v in the UK) Try a known-good power cable if you have one.