Simple Tech external memory 1.0 tb not registering all the sudden
First of all make sure that the USB port that you are using to connect it to your PC is a USB 2.0 port, and not USB 1.0.
Also if it came with an external power, connect it to the external power before putting on your PC.
This is because the voltage supplied by USB 1.0 is lower than that of USB 2.0 and therefore might not be enough to power up your USB Drive.
After making sure about this, power up your system, and plug the external drive, then Right-Click on my computer icon, select manage, then go to Disk Management Option.
On the Disk management option Page you should see ALL the drives installed on your system, including the hidden ones, so what you will just do is, try and locate the one representing your external drive, and right click on it. then select "Change Drive letter and Paths".
Give the drive any new, unique letter (i.e alphabet) different from the ones already on your system, and click on OK.
This should make your external Drive to be detected automatically.
Hope this helps you out.