What happens if PCIEcable isnt plugged correctly

[CrazieChipmunk]

So i just upgraded my new gpu and really didnt want to take out the psu and reinstall all the other cables so i as you can imagine i had a hard time getting the pcie cable in to the powersupply because of my shear laziness. I didnt hear anything click but as far as i can tell its in there and ive nudged it a bit to see if it would fall out but its firmly in there as far as i can tell, its the right way up i was jst wondering worst case circumstances if the cable isnt in correctly what could happen?

[mariushm]

Video card would not start and you'd get a message on screen saying "plug cable"

 

Worst case scenario, the pairs of wires that make good connection would carry the load while the poorly connected pairs would not... so the properly connected pairs of wires may be "overloaded" and overheat or something like that.