I am stumped, video cards not working

[Deerduke]

PC #1 video card doesnt work, so i put in a newer one, it wont work. But Video card #2 works fine on PC #2 , but not on PC #1 or #3
Video card #3 Works fine on PC #2, but again not on PC #1 or #3
so PC #1 and #3 motherboards have power, everything looks fine, its just video cards wont light up, I've tried different PCI slots, nothing, always the monitor says "HDMI power saving mode"
Any suggestions?

 

[rgd1101]

sure what the exact model of video card? and the spec for each PC, include make and model of the psu

 

[Deerduke]

MERGED QUESTION
Question from Deerduke : "Mboard not powering graphics cards"

I have two MSI mboards, one is old, another only a year old, neither used for gaming.
all of the sudden, the video cards stopped working, although they will work in other mboards.
Is it possible that a motherboard can lose PCIe connectivity?

oh, these are MSI AMD Militairy spec style Motherboards, and Nvidia GT 610 and 720 graphics cards, 16 gs RAM, AMD Black 4.2 and AMD 3.6, as well as a Corsair 750 Watt PSU that checks out.