Seagate FreeAgent Backup Drive Not Displaying Under My Computer

I hope this is the right place to post this.

I have a Seagate FreeAgent GoFlex 2TB external drive which is currently connected to my computer and working fine.

I recently purchased another external driver same as above but with 3TB.

When I plugged it in it automatically installed and said hardware found and is ready to use.

So I went to My Computer to find it but it doesn't display the 3TB drive. It only displays my 2TB drive.

If I look under Devices it lists two Seagate external drives.

When I go to my Backup Manager Program it tells me there are 2 drives to select for backup but one is UNKNOWN. That is my 3TB drive.

Does anyone know why it's not showing up on My Computer? I want to be able to click on the drive and chek my files once I've backed up.

Thanks.

[EDIT] I just found out that you can't run two of the same drives at the same time. I pulled my 2TB drive out and plugged the 3TB drive in and it comes up automatically. What a pain if I want to transfer files from my 2TB onto my 3TB drive.

I've heard some scuttle butt about this, with multiple external usb hdd's. For me, I would consider a hard drive enclosure and install a particular brand of hard drives and then connect via usb and either install some sort of home server software for backups or a plain back up software with automation built in for set it and forget on a daily, weekly backups. Or get one of those prebuilt home media servers for back ups, HP has a nice one.

This is worth a shot to try: plug in both drives and then type DISKMGMT.MSC into the start search box and see if you can't select, then right-click on the unknown drive and assign it a drive letter.

@ TrainableMan
I tried what you suggested but I can't select it because it doesn't show up at all in the list.

You should be logged on to an Administrator account.
Go to Control Panel\All Control Panel Items\Administrative Tools
Double click on Computer Management
Double click on Disk Management
If the unknown drive is listed there then right-click and assign it a drive letter.