My 250 GB I/O Magic USB external hard-drive randomly disconnects / ejects from the computer after between 2-30 minutes of use. When this happens, the blinking activity light on the front of the hard disk drive turns off; however, the disks can still be heard spinning. Unplugging and replugging in the USB does not reconnect the device and the activity light remains unlit. The only way to continue using it is to flip off and then on the power switch of the hard disk drive.
The hard disk drive was formatted with an MBR partition table and 2 NTFS volumes. I recently tried switching to GUID/GPT with two Mac OS Extended (Journaled), but the problem remains.
This error occurs with my new Macbook Pro with Mac OS X Snow Leopard as well as with my Dell Dimension E520 with Windows 7 Ultimate.
Best Answer
Sometimes Spotlight will cause this for some reason, but you said it also happens on Windows 7, so it leads me to believe it is a problem with the hardware.
Before considering to RMA the drive, try a different USB cable. It could be the External hard drive's USB port or some other internal component.