Desktop Hardware and Upgrade Questions

Helping a good friend out on upgrading his older desktop, an HP Pavilion P7-1110 "upgraded" to WIN 10 64bit https://support.hp.com/us-en/document/c03011622

Part listed him: Power supply, GPU, Ram, Cpu too hp listed qualifications via motherboard specs.

He got the 500w power supply and the GPU I picked out first, an ASUS 1060 6G, and we already ran into issues.

system runs fine with just new power supply ( no surprise)

With GPU in, it would get to a post-Post splash screen that just gives basic system information, but will not allow bios access, and ESC does nothing on the post-Post screen. Just the key press beeps. It is (was) sending some display, so I know the card is reading, but it just wont OS boot.

Had him install drivers from disk without card in, but system either isn't taking them without the card in, or not showing them. GeForce wont touch it without the card in, and the asus drivers were installed twice from disk, and the newest one once from website.

Tried having him boot with cables to GPU, and cables to motherboard GPU, neither take past the splash screen, and now wont go past a total black screen while the GPU is plugged in. I'm at a total loss. I know the GPU is PCI 16 ver3 and the MB PCI Port is ver2, but everything I have found says that is not a problem.

I'm working remotely with him, so I can't guarantee everything on layer 1, but it's not rocket surgery. Any Ideas?