|If this USB adaptor has a separate power supply it should still spin up when the power is applied without connecting to the USB port. All the USB power supply does is supply power for the USB adaptor, a maximum of 500 mA which is nowhere near enough to power and IDE hard dsik.|
Every IDE drive I have seen spins up as soon as power is applied, with or without anything connected to the data connector. That is because the drive controller is incorporated into the drive hardware. Applying power initialises the drive controller which spins up the disk,.
Try connecting the power without any connections to the USB at all. There may be a fault in the USB adaptor that is preventing the drive from spinning up.
Bear in mind that with modern hard drives it can be difficult to detect if the are spinning as they are so quiet. You may need to get it close to your ear.