It's possible the new GPU is dead.
I recently tried to upgrade my GPU from a gigabyte GTX 660 to an ASUS GTX 950-2G and ran into the problem that the new card wouldnt diplay.
I deleted the old drivers and installed the new ones for my card and nothing worked. ive also cleaned the pins on the GPU and updated my BIOS just in case something was conflicting.
To my knoledge the card pulls its power from the PCI slot so it doesnt need/have an 6-8 pin cable. i know my power supple is more than enough to power it and everything esle. and thats were in stuck at.
heres some relavent info:
motherboard- ASRock 970 Pro3
CPU- AMD FX-8320E
GPU- old: gigabyte gtx660/ new: asus gtx950-2G


Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic