Drive not accessible - access is denied

I'm locked out of my 1.5TB Maxtor basics USB desktop drive, with the above notification. There's no access at all to the volume, which shows as 0 bytes in size, although the drive is shared and appears to have the required security permissions (Admin and user rights). I have tried it from 2 different Win7 partitions, and it reads fine under XP. What gives? I need help!

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