disappearing esata disk

[k.hoppel@att.net]

Apology in advance for this probably not being a 64-bit specific problem: 
I am trying to attach a SATA disk using an external e-sata port 
(ASUS crosshair motherboard).  The disk works for a while after
booting, and I can mount and use the disk.  However, after a period
of time, ~10 minutes, the disk just disappears and cannot be accessed.
The disk drive feels like it is still spinning (external housing vibrates).
If I cycle the power or plug it into a different port, the disk is not
recognized - I have to reboot again to use the disk, until it disappears 
again.

Any ideas what the problem may be?

Thanks.