The blue light stays, but it is not discoverable

[josiahlee1998]

useless

 

[phil22]

Your information is very poor. The word "useless" tells us nothing about your problem.
Consequently, I am only guessing what is required since it's a common issue with external hard drives.

Go to Disk Management and assign a drive letter to it:
http://windows.microsoft.com/en-GB/windows-vista/Change-add-or-remove-a-drive-letter