I had this problem with my Maxtor one-store 160GIG external USB drive. My
computer is an older Dell Dimension 8200 so came with USB1.1 ports. I added
two USB2.0 PCI cards(each had 4 external USB ports). What I did to fix the
problem was unplug the HD from one card and plug it into the other card. I
have seen similar issues with optical mice that have to be plugged into
another port - usually the first port in an array of 2 or four ports that
are built into the mother boards. Case in point is the Dell Optiplex
GX270's and 620's.
v/r