Question PC takes multiple attempts to launch properly

[EnragedToad]

My PC (specs listed below) ever since upgrading my GPU from a GTX 690 to a RTX 3060ti takes multiple attempts to boot.

CPU	i7-4790k
MOTHERBOARD	GIGABYTE GA-Z97M-D3H
RAM	32 GB (DDR3)
GPU	RTX 3060ti (Zotac) *bought used, mention it later
PSU	Gold AX750 (Corsair)

Before I had installed the new GPU (RTX 3060ti), I had a GTX 690 and my PC would function flawlessly, no issues booting, booted instantly, etc.

After I first installed the RTX 3060ti, my PC launched fine and worked as expected, but after the first restart/shutdown (don't recall, did all of this in December), my monitor would display the no output signal text despite my case fans and GPU fans spinning and if my monitor did pick up anything, it would display a black screen with the blinking cursor symbol in the top left corner.

After struggling to have it launch, I figured out that if I left it long enough to run it would eventually launch but then my PC would perform horribly.

I did at one point put back the GTX 690 and it launched fine, put in the RTX 3060ti again and issues persisted.

Eventually I did get it running fine after multiple reboots, nothing wrong with performance.
Ever since then, my PC will not properly boot most times. What happens most frequently is that:

1. Either my monitor displays the no output message, sometimes if I leave it for a bit it'll progress to situation 2.
2. PC launches but displays the black screen with blinking cursor, sometimes if I leave my PC running long enough like this, it'll then project a completely black screen, then the BIOS splash, black screen with blinking cursor again and then Windows blue logo loading screen. *In most cases, if I do leave it like this it'll either freeze on the Windows blue logo loading screen and just turn off, if it does load pass Windows blue logo screen it might perform normally or it'll perform very slow and crash. The timing of these events vary, it could be really quick or really slow.

I just have to keep restarting it or shutting it down (before my PC launches properly, for some reason it just takes one click of the power button instead of press and hold, not sure if this is intentional but if my PC is running as it should be it requires a press and hold), eventually (can be from first attempt to several attempts) my PC will launch as it should, flashes bios splash and onto Windows blue logo loading screen instantly.

All in all, it's just a hit and miss when launching.

I have no idea what the issue can be, my PSU is sufficient enough for the GPU, I've tried reseating my RAM and testing it with only 2 in at a time, I've tried disabling Windows and Bios fast boot/startup, I've tried removing my USB devices, nothing.

Could my GPU simply be faulty? I did buy it used but I was shown it working perfectly fine and when my PC does launch it performs perfectly, the only issue is in the booting. I'm also aware that there's just a slight bottleneck with my GPU and CPU, could this be causing booting issues? My GPU uses a PCIE cable that features 2 x 8 pin connectors, only 8 pins are plugged in while the other just hang around, could that be an issue? And the the only other thing I could consider is could my motherboard be the cause, as it's not that new?

 

[kerberos_20]

this looks like firmware issue, gpu should have two firmwares, one for legacy bios and one for uefi bios
if your mainboard has CSM compatibility mode, try to enable/disable it to see if your issue changes, on old mainboard it can also be called windows 8 boot mode
switching this setting will make your boot drive not bootable, use random usb windows 10 boot media just to see if it boots from it or youll still get blinking cursor
if it boost from usb, then you will need to reinstall windows