This is straight from the Verbatim Website:
"Some computers do not provide enough power through the USB port to fully power the USB hard drive. If your computer’s USB port is not able to supply enough power, you may experience one of the following:
• The drive will have a blinking light, but it will not show up in My Computer (Windows).
• The drive will not successfully mount and show up on your desktop (Mac).
• Your Operating System may show an error message stating that a device
connected to the USB port has exceeded the power limit.
• The drive will frequently disconnect, appearing and then disappearing from My Computer.
• You hear the drive repeatedly spin up and down, or repeatedly click, but it never installs or mounts properly.
• The computer may freeze when the drive is connected or accessed.
• Windows may not recognize the device to install the correct drivers.
If you are experiencing any of these conditions, you may have a power issue. If your model drive came with an included USB Y-cable, use it to allow the combined power of TWO USB ports to power the drive. Otherwise, you may need the optional USB
Y-cable (96531, 96532, 96533, 96534), or optional AC Adapter (ACFLB)."
Have you tried plugging it into a different USB port? Do you have the above mentioned Y-cable?