Two Seagate external drives can't be seen simultaneously in Windows 7

Question

I have two external Seagate drives. The first is Flash Drive (FreeAgent Drive) and the second is (GoFlex drive) (USB 3.0).

I wanted to copy from one to the other while both were attached. They can't work together for some reasons. The one which was plugged first is shown (for example like: "J" drive) and the second is not shown at all but still visible from the Safely Remove and Eject MEdia tray, so I can eject them..

The system I'm running is Windows 7 64 bit and is up to date and I believe it's free from viruses according to Norton :D

They both are seen in the tray (Safely Remove and Eject Media).

They both work 100% seperately.

Answer 1

Copy and Pasted from…. Seagate KnowledgeBase
http://forums.seagate.com/t5/FreeAgent-Products/Using-two-Externals-at-once-one-won-t-show-up/m-p/78798/message-uid/78798/highlight/true#U78798
Answer By Xmustanguyx
Ok, just got my 2TB FreeAgent GOFlex Desk and plugged it into laptop. Formatted it works fine. Plugged my 500GB FreeAgent GO and NADA. Swapped just as you guys did and nothing, both worked independently and would not work together.
Here's what I did to fix: My system Gateway with WIN7 64BIT home premium. Externals are USB.
Right click My Computer then click Manage, then navigate to Storage>Disk Management. Find the external that shows a drive letter and change it to something else. (I don't think this is necessary but you can change it to what you like after you get them to work. This is what I did to get it to work.)
Next, Right Click the the drive that is not showing up, in my case I changed the 500GB to N:\ and the disk showing was Disk 2 Basic1863.02 GB.
Right click the GRAY area in the right hand side. Just under the red arrow that is pointing down. Under that you will see the error message if you hover over the HELP. It says, at least on mine "Offline (The disk is offline because it has a signature collision with another disk that is online)"
Now that you right clicked it select ONLINE and this will bring it online and automatically assign another drive letter. At this point you can change drive letters or whatever else.
Hope this helps,the post at Seagateis 3/4 down the page, but the whole page is on the subject.