Frustrating problem with Camcorders

We have 5 or 6 Canon camcorders in our Media Studies Department (a mix of MD205 and MV890) which are used to record footage, which is then transferred via FireWire to six Apple Macs (4 G3 iMacs and 2 Intel Core 2 iMacs). These have been working perfectly, until recently.

Suddenly, none of the cameras will connect with any of the computers. iMovie simply displays a 'No Camera Connected' error. The cameras also do not work on a Windows PC with a known good FireWire port and cable.

It seems infeasibly that 5 cameras of different ages could suddenly fail with the same problem, but I am now stuck with the troubleshooting. I'm hoping that someone may be able to offer some assistance with steps to try, either on Windows or Mac OS X or both.

Thanks.

Do they work in windows?
Have you install any updates recently?
Have you updated the OS?
What version if mac are you using?

Is there any common ground - for example, are you using the same fire-wire cable to test all of the cameras, and the computers? If so, it could be the cable.

> edit : "known good FireWire port and cable." - sorry, I missed that bit. <

Is there something special you need to do to get the cameras into the mode to connect to a PC (for example, on my old Canon DV camcorder I need to swivel a dial)... sometimes you do things unconsciously, and you might have forgotten.

Have the cameras all gone out to the same person/group recently - could the same fault-inducing incident have been done to them all? (It can happen, A tries to do X, it fails, they try it on the next camera etc. If X kills the camera...)

@FN-GM: Nope, don't work in Windows either. No recent updates (Macs not even online so can't have downloaded anything). Old Macs running OS X 10.3, new ones OS X 10.4.

@duncane: Have been doing exactly the same thing with the cameras that has been done all along which has always worked before. Thinking your theory might be possible about something having been done to all of the cameras - possibly one mac with a broken firewire which is messing up all the cameras?

A dodgy firewire on 1 Mac can screw things up elsewhere, I learnt that in my old school. You may have to check on each Mac to see where the fault lies