I have gone through two external hard drive enclosures and have had this issue with both, though not one from five years ago. When I turn off my Windows Vista Ultimate x64 system, the external hard drive enclosure (USB 2.0) powers down the hard drive, though stays on. When I turn my computer back on, the external hard drive remains off. The only way to get the drive to spin up again is to turn it off and wait for a few minutes before turning it back on.
This enclosure exhibits the same behavior regardless of what USB port it is hooked to. I have three USB ports on the chassis of my laptop and four more on a docking station.
This enclosure has always exhibited this behavior since I purchased it. The previous enclosure that I had seemed to have heat issues that caused it to spin down randomly and required you to put it in the refrigerator for a while to cool it down enough for it to spin up again. I'm not sure if this enclosure is exhibiting the same behavior or if this is unrelated.
Does anyone know what might be causing this problem?
Note: This is an enclosure for a 3.5in HDD that has a separate 120VAC power brick, so the computer itself is not powering the drive in any way (that I'm aware of).