If the computers are plugged into a UPS/Surge Protector, remove that as a potential problem and plug directly into the wall outlet.
If that doesn't fix the issue, then buy or swap in a known good power supply on one of the computers.
Hope this helps.
I have two dell Dimension 4700 pc and both seem to have suffered the same faith ie: refusing to power up. I use my my ULTRA 20/24 MOTHERBOARD tester to test each power supply and the reading is the same. The -5v light is the only light on the tester not lit up. Can anyone say what this means?
+5v, -5v +12v +5vSB PG -12V +3.3V
Each of these numbers have a green light above them and the -5v never lit up, could this means that my power supply is bad. Also only the power supply fan comes on. The cpu fan does not.
Dell dimension 4700, xp-pro,80ghd and 1gbMemory