HD needs more than 600mA to spin up, but USB 2.0 can only provide 500mA at most. HDD will either show a message, "ask for format," under insufficient power supply, or cannot be recognized by your computer. Insufficient power supply in the long term could damage HDD motors, causing data loss on your StoreJet.
If your computer does not have extra USB ports, we recommend that you purchase a Transcend USB Power Adapter HUB3 (more information: http://www.transcend-info.com/Products/No-402) in order to provide sufficient power.
Step1: plug the signal line of the Y-cable (the thicker line) into your computer USB port.
Step2: plug the power line (the thinner one) into Transcend HUB3.
Step3: plug the other end (the small end) of the Y-cable into the StoreJet.
Or you can try to use a USB HUB or other AC to USB adaptor for the additional supply power.
* The spec of the power supply output should be DC 5V and 1A.
Choose either of the approach mentioned above to have your StoreJet function normally.
Note: please make sure that you have plugged in the AC adapter if you use a notebook.