I'm running Debian Sarge and changed my repositories to Unstable and asked Synaptic to perform a smart upgrade. After this, I am unable to start X because of my mouse. Here is the relevant Xorg log piece:

EE) xf86OpenSerial: Cannot open device /dev/input/mice
No such device.
(EE) Configured Mouse: cannot open input device
(EE) PreInit failed for input device "Configured Mouse"
(II) UnloadModule: "mouse"
(WW) No core pointer registered
(II) XINPUT: Adding extended input device "Generic Keyboard" (type: KEYBOARD)
(II) XINPUT: Adding extended input device "NVIDIA Event Handler" (type: Other)
No core pointer

Fatal server error:
failed to initialize core devices

try to reconfigure your xserver,

# dpkg-reconfigure xserver-xorg

I tried that, and again when I tried to start x, it gave me the same output.

Your xserver-xorg cannot probe & configure your mouse properly. Try to change your mouse device manually (in your /etc/X11/xorg.conf), i.e. /dev/psaux

regards

Well, it's a USB mouse and X worked before I did this upgrade, but it doesn't work now. The settings appear to be the same... I don't know. :-\

If I put in /dev/psaux as the device it will boot into X except for the fact that I don't have use of my mouse because it's a USB mouse!