Did you rule out obvious possible reasons like power breaker or bad power bar?
Did you have any power surges lately? Power outages, electrical work being done near or in your house?
Is everything else working fine in the house? TV, radio, sound system, etc.
Also, did you try disconnecting the machines from all external equipment?
Turn off printers, hard disks, network, including the wifi network, etc.
If you have an electrical tester, see what level of power you have on your outlets.
Should be between 110 and 120v.
When I say it should be between 110 and 120v, that is if you are in north America.
If in Europe, it should be around 220 to 240V
Many Asian countries are on 100v.
Do all of the machines power up but fail to boot?
Is there a power light turning on on all of them?
If nothing at all is happening, it could be the power supplies that got fried by a power surge or even the hard disks.