Non working PCI-E slot on Asus P8Z68-V GEN3 Please help :)

[LukaTCE]

Hi main PCI-E slot stopped to work today
Yesterday it worked normally everything then I turned it off and when i turned it on at morning it didn't worked.
I didn't moved anything inside PC.
I switched gfx on second slot and it work. I checked if any pins are broken inside first slot and there are none.
Any idea why it would stop to work ? Maybe it have PSU to do something with that ? Fan on PSU started to make weird noises.

Second slot is only PCI-E 2.0 x8 but it should be PCI-E 3.0 x8 So I would get similar bandwidth as PCI-E 2.0 x16 7880MB/s vs 8GB/s
Tested in Furmark and GPU runs at 99% I have to test with games. x8 is probably not enough for gaming right ?
How I can set it to PCI-E 3.0 at second slot. I remember when I had on first it worked 3.0 and then a year later it showed only 2.0
How I can check if first PCI-E slot is broken ? any pin check at bottom of mobo with multimeter ?
Mobo is Asus P8Z68-V GEN3 3402 bios and GPU is Gigabyte GV-R928XOC-3GD rev1 and PSU is LC Power 850w (ye I know bad PSU)
Edit: Forgot to mention one fan didn't turned on at first slot (worked only manual turn) and in second slot it turn on automatically

Mobo manual if in any help https://dlcdnets.asus.com/pub/ASUS/m...Z68-V_GEN3.pdf

Edit: So I lose max 3-4% at PCE-E 2.0 x8 ?
I forgot to mention.
At same time SSD didn't worked after. First it showed BSOD error and then suddenly even SSD stopped to work.
BSOD: KERNEL DATA INPAGE ERROR SSD working now with no data loss.
After I just put PC down into lying down position and SSD started to work. Weird as HDD worked while SSD didn't in standing up position.
I rechecked cables and everything was connected. I don't get it how PCI-E slot stopped to work it might be connection on mobo. I wasn't moving PC since it was working.
As there is only 3-4% difference I will use just second slot now. Probably isn't worth to replace mobo just because of that, right ?

Taking everything off takes just too much time as case is too small and SilverArrow cooler is complicated to take off and install again.
Case Enermax Chakra is just too small and PSU is on top and it's way too small space to remove everything with big mobo

Edit 3: After that again SSD stopped to work again and HDD couldn't be recognized now both are working. All happened after Windows 10 update to new build. I understand for data but SSD didn't worked at all I also don't have a clue why at same time GPU slot would stop to work ? better I replace that PSU it's like 10 years old
SSD Utility also gave me a warning for high voltage.

[Firewrath9]

rma

[LukaTCE]

I can't RMA it mobo is too out it's out of warranty.

Second slot is making GPU heat too much. Any other idea why would first slot just stop to work without any physical damage ? PC didn't fall or something I even didn't moved it