mouse/keyboard not responding under Xorg

[michael]

I've not managed to define precisely when I get problems but I'm  
noticing
the following symptoms and was wondering if some kind soul would help me
debug what's going on in order to get to a solution? Thanks, Michael

set-up: etch, gnome (eg gnome-core 2.14.3.6), metacity 2.14.5-4 and
Dell/Logitech USB optical mouse (seems to work fine in WinXP), with
nVidia graphics card/TwinView and 2 monitors (diff resolutions)

symptoms (occasional and not sure how to repeat)

a) double clicking won't select anything
b) in evolution, clicking on a new message or folder has no effect
c) the cursor (arrowhead) disappears - if I set prefs to show cursor by
depressing 'CNTL' I get the moving rectangles but there's no cursor
there)
d) focus doesn't move to new window (as it should and usually does)

I think the following is also a symptom but not 100% sure:
e) doing ALT-TAB to move between windows does nothing on very first
ALT-TAB

If it's the keyboard that's failed then using I also cannot get Gnome  
menus (it selects the top level but nothing is shown) but can use the  
mouse to open more new app/windows and then at some pt the keyboard  
seems to be 'reset' such that it starts working again.

I've tried KDE and that also has the keyboard not responding (eg if I  
try to switch desktops quickly then the keyboard stops responding) -  
opening the control centre and changing options in there appears to  
'reset' the keyboard.

Any thoughts either on what's going on or how to debug it to narrow  
down the issues? I've asked on the Debian mailing list but am still  
stuck. I've had this line in my xorg.conf re Mouse device:
	Option         "Protocol" "ImPS/2"
although it's a USB mouse I'm using, but commenting it out I still see the same issues


Thanks, M