External Hard Drive Stop showing up on Explorer

Hi, I have a 2.5" 10G Fujitsu hard drive with USB enclosure. The
problem starts after I was trying to copy files over & suddenly it lost
connection. The progress stop responding. I restart the computer &
replug the enclosure but it no longer showing up on Explorer. I went to
Disk Management and couldn't see it as well. Remove it & plug it in
another computer that's running Window XP. Immediately it shows up both
in Explorer & Disk Management. I backup all the files, reformat the
drive, and scan disk. Everything looks fine. Then I plug the drive
back to the original computer that's running Vista Ultimate. After it
said installing the new device & ready to use. I open explorer & it
didn't show up. Go to Disk Management, it shows up as Disk 1 with Blue
label. However, it doesn't has any drive letter assigned. I right
click and it only has 1 option = HELP. When I plug it back to XP
computer, it works perfectly fine.

I've tried the following solution:
1) unplug all device attached to USB, uninstall all USB drive, restart
computer
2) try plug in different USB port
3) try reformat the drive in XP again & assign a different drive letter

I've look through every where but I simply can't find any solution.
Can someone please help me on this? Greatly appreciated!!!