problem with usb disks

[David Jansen]

On most machines running FC2 a usb disk (flash type, or external
harddisk) just shows up when plugged in, but so far I have found on a
couple of machines that nothing happens. No entries in the logs when 
the device gets plugged in, nothing in /proc/bus/usb/devices, and it
makes no difference whether the usb disk is present at boot time or
plugged in later.

So far I have determined the following: 
- when FC1 was installed on these computers, usb disks worked without problems
- the USB mouse is working also
- USB modules are loaded
- no changes in /proc/bus/usb/ or /sys/bus/usb when the device is
plugged in or removed

Does anyone have a suggestion what can be the problem on those
computers? It looks like the kernel doesn't see the hotplug event on
those systems.

David Jansen