black screen with vertical white line down middle!

That appearance usually means something in the video circuitry has seriously failed and the entire image has collapsed into the single line. I had that happen on an Apple CRT external monitor and it was accompanied by a pop, a curl of smoke and a burning electronics smell. I was looking at the monitor when it failed so got to experience all the sights, sounds and odors.

This is NOT a DIY repair (difficult take-apart and high-voltage dangers) and it would probably cost much more than the computer is worth to have it fixed at a computer shop. It's likely you could buy a used or refurbed G5 iMac or a Mac Mini for what the repairs would cost. I would not try to turn on the computer unless you get it fixed. Pull the plug to protect against a fire hazard.

I looked to see if there was a Mac User Group (MUG) in Scotland, thinking someone there might be willing to do some pro bono work for your school. Unfortunately, none were listed.