System won't boot/post with GFX card in PCIe 3.0 16x but runs fine in either 16x 3.0 or 8x 3.0!?

I haven't posted much, if at all on this forum and this thing is driving me nuts. Please bear with me, this might be poorly written as I'm quite exhausted from running from store to store for help.

I recently purchased a new processor (i5 4670K) and mobo (MSI Z87-G45 Gaming) to fit it in since my old rig seemed to bottleneck my HD7950 graphics card (Gigabyte Windforce 3x).
It didn't boot at the start. It didn't even post and my monitor did not seem to get any signal.
After a lot of tinkering, reseating, and cussing I got it to boot with the GFX card in the 2nd slot. Installed win7 and got the drivers running. To my own detriment it only ran on 8x PCI3.
After another long episode of tinkering I managed to try a different, older graphics card (HD5xxx) which booted fine from the start but only supported PCIe 2.0. I tested yet another card (HD7750) in PCIe 3.0 mode and it ran fine.

I finally set the 1st 16x slot to PCIe 2.0 and was able to boot and run stable with my own graphics card.

I honestly have no idea if my brand new mobo is faulty or my 7months old HD7950 is...

I'd really appreciate some help.

Edit: I forgot to mention I flashed the BIOS to v1.6 in an attempt to remedy this.
2 answers Last reply
More about system boot post gfx card pcie 16x runs fine 16x
  1. Maybe you should consider updating the bios of your graphic card too.

    If that doesn't solve, ask for support to both your motherboard and graphic card manufacturer's, once I had a similar problem and they solved it to me.
  2. Nuno Silva said:
    Maybe you should consider updating the bios of your graphic card too.

    Thanks, I'm not really confident on what BIOS version of my gfx card I should try...

    Edit: tested the card in a friend's system and showed the same symptoms. Seems to me the card is faulty. I'm still unsure whether a card-BIOS update would work but I'm hesitant to try. GPU-Z reports a 015.026 BIOS version and it seems it's the latest from Gigabyte's site. A 015.031 version is available but I'm not sure if the card allows that update judging from the series.
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