External USB harddrive must be re-activated after every boot

Hi,

Got myself an external case and fitted in my 120GB disc. This case is
attached to my server running WinXP Pro sp1 by USB2.0. The drive is
recognized by the hardware manager but not by the file system. I have
to go into the drive manager where is is recognized. But I need to
're-activate' this disc everytime after a reboot before the filesystem
will recognize the disc (and a driveletter is assigned)

The disc is formatted with a single NTFS partion and it's a dynamic
disc.

Anyone help?

-Edo