From the Disk management help Vista:
Initialize New Disks
Backup Operator or Administrator is the minimum membership required.
To initialize new disks
In Disk Management, right-click the disk you want to initialize, and then click Initialize Disk.
In the Initialize Disk dialog box, select the disk(s) to initialize. You can select whether to use the master boot record (MBR) or GUID partition table (GPT) partition style.
The disk is initialized as a basic disk.
New disks appear as Not Initialized. Before you can use a disk, you must first initialize it. If you start Disk Management after adding a disk, the Initialize Disk Wizard appears so you can initialize the disk.
I should have read better . I think you may have done the above. Try a new USB cable.