does the usb port work on the laptop? Does the external hard disk work on other computers? You need to provide more information.
How To Ask Questions The Smart Way
Before asking a technical question do the following:
Try to find an answer by searching the forum.
Try to find an answer by searching the Web.
Try to find an answer by reading the manual.
Try to find an answer by reading a FAQ.
Be precise and informative about your problem
Describe the symptoms of your problem or bug carefully and clearly.
Describe the environment in which it occurs (machine, OS, application, whatever). Provide your vendor's distribution and release level (e.g.: “Windows XP SP1”, “Ubuntu 12.04 32bit”, etc.).
Describe the research you did to try and understand the problem before you asked the question.
Describe the diagnostic steps you took to try and pin down the problem yourself before you asked the question.
Describe any possibly relevant recent changes in your computer or software configuration.
If at all possible, provide a way to reproduce the problem in a controlled environment.