Gnome Shell Problems

[Chris Baines <cbaines8 gmail com>]

I have gnome-shell version 2.91.92 installed on Debian
Sid/Experimental. When I try to login the screen appears blank and the
processor and memory usage jumps sky high. When I login using the twm
(Tab Window Manager) and try to start gnome shell from bash to get
some debug output it refuses to start saying:
chris@chris-desktop:~$ gnome-shell --replace
Window manager warning: Screen 0 on display ":0.0" already has a window manager

How do I go about debugging the issue here, I have looked at the
commands listed on the https://live.gnome.org/GnomeShell/Debugging
page, but as I don't have a working gnome session, I cannot use them.

Thanks,

Chris