When there is some issue with the file system on that drive or it has some autorun software that is incompatible. You didn't reveal if you partitioned and formatted it on this Windows 7 machine but that's how I fixed a similar drive here.
There's another issue where duplicate drive letters can cause this. Easy to fix. Head to disk management and assign it a letter.
Every time I plug in eGo Helium 320 GB USB 2.0 Portable Hard Drive into the USB on my Gateway laptop, I go to my computer, and there is no indication of my Portable Hard Drive.
However, if I go to control panel, and then to view devices and printers... The folder indicates the devices that are attached or working on my laptop.
Its indicating that there is a USB Ata/Atapi bridge that is attached to my computer, which is the eGo Helium 320 GB USB 2.0 Portable Hard Drive, but it will not allow me to use it and it will not show the hard drive in my computer.
Does anyone have an ideal why this is happen and how it can be fix? I would appreciate it greatly.