The power supplies on that model are known to fail, so that may be what died. As for ethernet, sometimes the computer won't autonegotiate a suitable connection with the central hub, depending on what's in your schools' wiring closet. For that, go to the Network control panel, Advanced, Ethernet, and configure manually starting with 10base-T half duplex and see if that will connect. If that works, try 100base-TX half-duplex, then 100base-TX full-duplex, flow-control and see what you can get. The G4s ought to have automatic polarity sensing, so you shouldn't have to worry about crossover or straight cat 5 cables, but that can be an issue with older Macs and PCs.