Hour-glass! That sounds like Windows not OS X!
Just on general principle completely disconnect your Macs from all power sources and let them stay that way for anywhere from 15 to 30 minutes. Sometimes that will allow internal circuits that have been "choked" by the power surge to drain and reset. Depending on what G4 you have you can also open up the case and press the CUDA switch (see your owners manual for instructions on where to find it.)
On the theory your non-volatile RAM may have been scrambled by the power surge try booting while simultaneously holding down Command+Option+P+R and holding those keys until your Mac chimes at least four times.
If that does not clear the problem, reboot while holding down Command+Option+O+F to boot into open firmware then at the prompt O> enter the following:
reset-nvram and Press Return
reset-all Press Return
If that does not work try rebooting from the OS X install CD/DVD. (If you can't boot from the install CD/DVD it is probable the surge fried some internals and you need the services of a certified Apple repair technician.
If you can boot from the CD/DVD, on the installer menu select Disk Utility and run the Repair Disk function again and again until no errors are found or DU reports unrepairable errors. If you get to this point post back here for the next steps to take.
As soon as you are back up and running, go to the nearest computer store or office supply and purchase a good uninterruptable power supply for each of your Macs. Get UPSs with a minimum of 700 volt-amps.