I'll keep this simple. I have 3 GTX 780's, 1 GTX 780 ti,and 1 GTX 760. I also have multiple gaming rigs. I have more gpus than those but it should eliminate a lot of questions. Ive used every combination between them. I have an EVGA GTX 780 that will mostly freeze on or after splash screen. I can't enter my bios and windows will not load. It has only gotten as far as the windows logo but thats it. If I try to enter my bios it freezes and so does the keyboard. No num lock or caps can be turned on or off. Now, if I just let it boot it will more than likely either stop at the windows loading screen or go blank after the splash screen and when doing that the keyboard doesn't freeze I can hit control-alt-delete and reboot. I get nowhere. I can't even run safe mode or even get to that point. Okay now with that said this is where things get weird. I've been doing computers for about 15 years and I've never seen this. If I install two graphics cards and the one that is messing up(EVGA GTX 780) in the secondary PCIe slot the graphics card works. I'm not running them SLI or anything like that. It would probably be a typical setup for somebody that does video editing the cards are not linked. I can have one monitor running off of One graphics card and the bad one running off another monitor. I have done extensive testing benchmarks gaming and verified that I am using the graphics card that does not want to boot. The card works flawlessly when using to card but thats only to get windows to load. I don't think its a windows problem but I could be wring. So my question is what could be causing the card to fail? The only way to get it working is to get into windows and thats only buy running 2 card to get past post and windows loading. Once thats done it works great.

Update:

I noticed that in GPU-Z it's showing its running @pcie x1 v1.1 even though the slot should be I believe pics x8. Perforamce isnt where it should he for a 780 but it still gets close to my other 780s. Basically it's running at bare minimum. Also the only way to get it to work with 2 cards It seems you have to install a 700 series GTX for it to work. I tried 600 series and an older GT. I assume because it allows the system to detect the same drivers.

Ok awesome I'll try that. It did cross my mind to do that. I just got it and owner said it had been sitting in storage so I'll def try that. I honestly think there is a bad fuse, mosfet, etc.

MoBo bios is up to date and i re-flashed the GPU which was the first thing i did. I've been reading and seen where a boot fuse was an issue on some cards. If I could get a hold of a schematic for this card I could definitely troubleshoot it. I'm pretty sure there is something physically wrong after everything I've checked and did. Is a fuse "a thing" on the 780s? 

destroyer4586
MoBo bios is up to date and i re-flashed the GPU which was the first thing i did. I've been reading and seen where a boot fuse was an issue on some cards. If I could get a hold of a schematic for this card I could definitely troubleshoot it. I'm pretty sure there is something physically wrong after everything I've checked and did. Is a fuse "a thing" on the 780s? 

No idea but it would def make sense to have one around the power area, but if a fuse was blown the card wouldn't do anything cause a fuse acts like a switch and disconnects the electrical path.. The only other way to approach it is to get a multimeter and set it to ohms, or continuity checks, to check resistance and see if you get any hits. You can try a continuity tester but it may not be precise enough to do what you want here. Im also wondering if when you put the second bad card in with the first good card, could it be that the first card sets up the lower card to sit correctly in the motherboard slot?!? Sometimes some cases can tweak the way your card sits and make crazy things like this happen, especially if you put in both screws to secure it and it pulls the card at all.