It seems that a power spike may have caused a slight corruption of the file system, which was causing it to freeze while trying to initialize the firewall system.
After working this out with Daniel over the phone, I was able to temporarily disable the firewall software so that it could talk to the outside world again, and then Daniel was able to connect from his machine and fix the problem. A quick reboot later, and all was well.
Of course, we couldn't leave well enough alone, now could we?
The Linux file system keeps a track of everything it does in a journal, so that if anything happens with the file system, it can make a good effort of rebuilding it. Lancelot was set to journal what it did, but not the data it did it with. Daniel decided to upgrade the journaling so that it recorded everything, so that if it happened again (and it most likely will, considering how lousy the power is at my place) it should be able to recover completely itself, with no outside assistance.
So Daniel made the changes from his place, and told me that they'll come into effect after the next reboot. I decided to reboot straight away, because I didn't want to tempt fate.
So I reboot, and Lancelot tells me that the file system is now read-only, and nothing works!
We decided to call it quits (this was still Friday night) and wait until the morning, because Daniel would need physical access to the machine to fix this small blunder. Oops!
He turns up Saturday morning, and we run into a few other problems. To revert Lancelot back to the working Journal mode, he needs to be able to do one of two things.
Either create a repair floppy on one of my windows machines from the Linux CD, or insert the Linux CD into Lancelot itself and repair it directly.
This is when I find out that the CD-ROM on Lancelot is broken, as is the only floppy drive on either of the windows machines. Eventually I pull Lancelot apart, pull out the old CD-ROM drive, replace it with the CD burner (the only spare I had), fix Lancelot, and the remove the burner again.
So after many head-aches Lancelot is talking again, and Daniel knows not to try and change the Journal type of a Debian file system like that again.
Ain't computers wonderful?