Disconnecting external hard drive

I have a problem with an external disk WD My book. The drive itself works, but sometimes, especially when I leave the computer on a time without touching them (if I m not a half hours) and return the disc is not found in the workplace ( "computer" because I'm in vista) or in the Device Manager. The solutions in this case are shut down and restart the disc, which not always work, in which case I have to reboot the pc. All my drivers are up to date yet. Can you help s you like it?

Hello, welcome to the forum.

In Device Manager, double click on your device or its controller firewire and see if a case of this type can be checked:

I do not have access to a dialog box like that on Vista. or at least I do not know where to find it .

Ok, in power management (panel config), look the time to extinction of hard drives, it can play.

there is the "power options" but nothing to change external drives unfortunately