Vista - External USB Drives not being detected by Vista Ultimate Full Release Ver.

Help! I have 2 External USB hard drives. 1 80GB Hammer Storage Drive and a
brand new WD My Book 250GB USB Drive. Both drives are found with no problem
on Vista Business on my laptop but for some reason Vista Ultimate on my
Desktop does not recognize the devices. I tried manually selecting the disk
drivers that the business version is using but no look. Just comes up with
either unknown device or USB Mass Storage Device but its still not found.
Device manager doesn't show the drive and rescanning doesn't help. I
checked my BIOS to see if it is something in their but I can't seem to find
anything that would create this problem. any assistance would be greatly
appreciated.

Thanks again in advance for the help.
Joe