Windows XP Pro has crashed and fails to start. It gets to the Windows
screen and the progress bar just keeps going - nowhere.

The disk access light is on full-time. Jusst prior to this everything
seemed to be really slow.

Trying to start in safe mode, safe with dos, or sfae with networking
shows that it hangs when loading

C:\windows\system32\drivers\btkrnl.sys

Using start with boot logging has no effect.

Unplugging my Logitech BT combo has no effect.

I think it had just downloaded and installed a Windows update. This
update had failed to install and just kept on downloading

and the Windows help people had suggested trying to run some command
like "oc qc system=" plus some other stuff. This seemed

to get the update to install but now I wish it hadn't!

I can't get in to see what the email said!

Help!

Cheers