I know you have probably seen one of these threads over a million times but I've searched and tried everything but it doesn't work. I have a 40gb external hard drive I bought, it worked fine at first, just plugged it in and it detected it and was able to transfer all my files to the drive as I was about to reboot my laptop to factory standard. Now I rebooted and it all worked fine still, still being able to access all my files. Now I changed the name to external jus by clicking on the name in my computer. I turned the laptop off and turned it back on and now its detecting that I have plugged it in and is all working fine but I can't find it in my computer, absolutely nowhere to be seen, even in the drop down. I have been to the disk management and found it as Disk 1 and there is no right click option to be able to rename the disk drive to a letter.
As you can see below this is what I can see. Have I lost all my files as I was transferring them to this drive and don't have any more copies anywhere else.
According to diskmanager the disk is not initialized. Id suggest if this drive was working and now its done this you have either corrupted the file system (via unsafe removal etc.) or the drive itself is dying.
Now if you have nothing stored on this that you need, try initializing the disk (which is done by right clicking on the "not initialized" section to the left of where you have right clicked. This will mean you will have to partition the drive again and all info will be lost.
If you have data on the drive try booting a boot cd i use WinUBCD which can be found with a google search and run a chkdsk on the drive (if it gets a drive letter). The other way is to try a fixmbr and fixboot in the windows recovery (bootcd) although this can compromise data on the drive also and im not sure if this can be done with a USB harddrive.
If the drive continues to disappear like this and loose partition information the drive is dying and should be replaced