Drive letter resets!! Need Help!

I have a 1 TB external hard drive I formatted to FAT32. My drive works perfectly but everytime I turn off then on it gives me this message when I try to get into it:

z: drive Refers to a location that is unavailable. It could be on a hard drive on this computer, or, on a network. Check to make sure that the disk is properly inserted, or that you car connedted to the internet or your network, and then try again. If it stil can not be located, the information might have been moved to a different location.

In order for me to get into my external drive when it gives me this msg I will go into my device management and give my drive a new letter. My drive is making me manually give it a new letter to get into it. How do I fix this???? Is there a way that it does it automatically?

Also when I turn off my EHD the drive icon will still show in MY COMPUTERS. When I turn it on it will still show even while I give my new a new letter.

Thanks for the for the reply but I know how to change, remove, and add the lettter. My problem is every time I turn off/on my EHD I need to manually add a new letter just to get into my drive. Is there a way it does this automatically? My first EHD is very simply, I plug it in to my laptop turn it on and the drive will pop up in MY Computer. This is my 2nd HDD and its giving me a hard time. My laptop recognizes the drive because it sounds me when I turn it on but it does not pop up automatically in My Computer.

Yes, I used a third Party tool to format to Fat32.

You formatted to Fat 32, why?
Check this out.
Convert a hard disk or partition to FAT32 format

The PS3 only recognizes HDD that are FAT32 Format.