Solved USB HD Not Recognized

I shut down my PC (Vista 64) with both my external USB HD and a USB Thumb drive attached. On reboot the USB HD is not recognized. I moved it to another PC with the same cord and it is recognized and all the data is there. If I shut it down or turn it on you get the windows sound, but it is not picked up in the control panel , nor does auto play start.

Any help would be appreciated

Additional Info; In device manager the USB drive is detected as"USB MASS Storage Device" Under "Universal Serial Controller" but not display in My PC.

Resolved it; I went into Disk management and discovered that the USB HD was listed as a healthy volume without a drive letter. (WTF windows). I assigned it a drive letter and all is well.. auto play ran and the drive is picked up in My Computer.