External USB Hard Drive not mounting

I recently bought an external enclosure for a hard drive so I can backup my laptop.  I went through all the normal procedure to connect it, but it doesn't show up on My Computer.

I checked in the Device Manager and it shows up under Disk Drives.

I checked in Computer Management and I see the disk under Disk Management, but it hasn't been assigned a drive letter.  I manually assigned a drive letter which now shows up in the Disk Management window, but I still don't see it in My Computer.  I'm not able to choose Open or Explore for that drive in Computer Management.  It gives me a drive not found error.

I tried deleting the partition, recreating it and formatting it, but no luck.  I tried restarting my computer

as it requested, but still no luck.  I've downloaded the latest BIOS update from Dell.com.

I've set the hard drive to be Master, not Slave, using the jumpers on the drive.

I'm running Windows XP Professional with Service Pack 2 loaded.  My computer

is a Dell Latitude D620.

Any help is appreciated!