Hmmm .... dig big hole in ground and toss in offending computers
Seriously, you probably want ferrite snap on chokes on all the wires exiting computer. A power line filter may also help. If the computers have metal cases, you might remove cover and scrape off paint where screws make contact. If you have computers with plastic cases, get out your wallet and buy some silver paint (conductive) and apply to inside of cover. When all else fails, build a brass screen enclosure around the computer !