Before removal of your USB external drive, it is a good practice to click on the "Safely Remove Hardware" tool located on the right hand bottom of the window.

Doing so will allow the system to properly closed all the systems files, finish all the tasks and properly wrap up all the folders and rewrite the MBR so that the next connection, the computer will be able to find where are the files located.

What happens if the "Safely Remove Hardware" is busy.

On some ocassions, the tool remains busy, wait a while for it to finish the tasks. The biggest culprit of "device cannot be recognised" is because the external harddisk was pulled out before it has finished the jobs.

Some users in one action, copy the whole directory from an old drive to the new USB external drive. Well, the users may be transferring more than 100GB or 200GB in one action. Surely this will take some time, sometimes as long as 2 hours or longer iif the old drives is pockmarked with bad sectors.

Wait patiently for the drive to finish its job. If it is still busy, and you think your drive might hang, do not pull out the drive. You can do the following

1 Press the "Control, Alt and Delete" keys all at once to bring out the Task Manager. See what is not responding and end the process.

2 If it is still not responding, do a proper shut down. The computer may take some time to shut down. See the HDD lights. If it is blinking, means the system is still working on the files, give it some time before taking the next action.

3. If all else fails, then you do a force shut down. Doing so, your system will leave whatever tasks uncompleted and just turn off.

In your next boot up, do a check disk on your drives to repair and remove any unfinished work and repair the files structure.

Find out what was wrong in the first place and take action to rectify the problem.