Hard disk not opening

Does the hard drive work on other computers?
Have you tried another USB port?
What operating system are you running?
Does your hard drive need extra power, or does it just have the USB?

Is this a brand new disk? If so, you'll probably have to partition and format it before you'll be able to use it:

Click "Start" --> right-click "Computer" and select "Manage".

Click "Disk Management" in the left pane.

Scroll down to the BOTTOM of the MIDDLE pane.

You should see your new disk there with a label such as "Disk 1" or "Disk 2", etc. Right-click on the label in order to create a new volume (which partitions the drive) and then again to format it.

Once it's formatted Windows will assign the next available drive letter to it and then it will appear in Windows Explorer.