External drive problem

Did the hard drive come in the enclosure? (Is the hard drive supported by the extrenal enclosure) Does it work when plugged into another computer and have you tried using another cable?
Did it come in the enclosure? Try another cable
Did it work when plugged into another computer?
Yes - Windows Drivers
No - Try another enclosure or cable
Did it work with another cable?
Yes - Problem Solved
No - Try another enclosure with the new cable
try whichever of these and see if it helps. please respond here with what happens wether it works or not.
Another option by the way is to check what happens when you take the hard drive out of the enclosure and install it inside the computer as an internal Hard Drive. If that works then it isn't the hard drive atleast. I will away to see what happens.

If the drive is brand new, then it is likely that it needs to be formatted. If it is an old drive you have used before, then it is highly likely that the drive has failed. I suggest you format the drive and see if that helps.

Select USB Portable External Drive to Boot Priority on the BIOS...
Inserting Operating System also needed.
Good luck!

It seems your pen drive is not formatted or corrupted. Take it to some other pc go to run and type cmd check what is the drive letter that pc has given to it and type format H: or whatever it is your pen drive may recover. Else you have to get a new one.

If the device is recognized and not listed as a driver in the Explorer, then the disk is not recognized as having been partitioned and formatted. You can use the Disk Manager to see if there is anything listed on the disk.
Start - > right-click My Computer -> Properties
In the management console, go to disk management and check your disks. The external disk should be there and then you can see the partitions and drives assigned to it.
If there is nothing on it, your MBR could be damaged, which needs to be restored.

Alternatively you could partition and format it, but then you'd loose the data on it, so that is a last resort.

I think a program called Acronis Disk Director Suite can restore MBR's. Have a look at this external hard disk troubleshooting article.

Please insert a disk into drive

right click my computer.
click manage
selest disk management
right click to drive-H
select change path 7 name of drive
change it to any letter except lettur used for your other drives
thats it it is done.

if u are using a external hard disk case with the normal hard disk
try connecting your hard disk with a new casing.
if it is made as a external hard disk change the cable .
because after a few time usage the cable will not be quite good as new.
After inserting the usb cable in your pc if it shows any warning
information, or any message just give me that too for exact solution

The hard drive was originally formatted for a PC and I was using it with Mac products. I had to delete all the information on the hard drive so that I could reformat the external hard drive to work with my Macbook Pro. 

Make sure there is nothing inside before inserting a new disk.

Also, try to get one of those disk drive head cleaning disk and run it.