Question PC won't start with my nvidia 3060ti connected to the power supply

[helx]

Hello!
I just bought a new nvidia 3060ti founders edition GPU.
I put the new card in my PC, replacing an old nvidia 750ti GPU. After installing it and connecting it to the power supply I started my PC.
At first, everything appeared to be working normal, I run some tests with Furmark and started to play some games.
After about 30 or 40 minutes I quit the game and left the PC on. Not long after getting up from the PC, the fans from the GPU just started to spin really fast (faster than when I run Furmark) and I didn't know why, so I went to the computer and shut it down from the button (I kept pressing the power button till it completely shut down).
I started the PC again and tried to run the last game I played (Dota 2) and then close it, just to see if the problem occurs again. After closing the game, though the fans didn't start to behave abnormally, the PC completely shut down.
After that I tried to power the PC back on, but when I press the power button, only my RGB from my RAM memory turns on and the computer does not.
I discovered that if I disconnect the power cables from the GPU, the PC starts normally. I even put the old GPU back and everything is normal, but with the 3060ti the PC just doesn't start.
I have a 850W Corsair RM850x 80+ Gold in my PC and I tried to change the cables but with no result. I even tried to change the PSU with a Corsair RM550x 80+ Gold (550W), but this time not even the RAM RGB turns on.
Any idea of what went wrong with the GPU and possible fixes would be very appreciated.

Later edit:
PC specs are as follows:
CPU: AMD Ryzen 5 5600x 3.7GHz
CPU cooler: ARCTIC Freezer 34 eSports DUO
Motherboard: GIGABYTE B550M DS3H
RAM: Corsair Vengeance RGB PRO 16GB, DDR4, 3600MHz, CL18, Dual Channel Kit
Storage: Samsung 970 EVO Plus 1TB NVMe M2
PSU: Corsair RM850x, 80 Plus Gold, 850W Fully Modular
Chassis: ENDORFY Signum 300 ARGB
OS: Windows 10 Pro
Monitor: LED IPS LG 29'' Full HD, 75Hz, 5ms, HDR10, sRGB 99%, AMD FreeSync™, HDMI, 29WP500-B.AEU
GPU: Nvidia RTX 3060Ti Founders Edition
BIOS Version/Date: American Megatrends International, LLC. F1, 07.12.2022

The monitor was bought about 2 years ago.
All the PC components, except the PSU and the GPU, were bought last year in june.
The Corsair RM850x, 80 Plus Gold, 850W Fully Modular is new, I bought it like a week ago, from the store.
The GPU is second hand and I just bought it.

More info about the GPU:
Given the fact that is second hand, before I bought it I ran some tests.
I used GPUZ to verify that is in fact an RTX 3060Ti and that specs correspond to the ones on the producer site, then I ran for about 20 minutes Furmark while keeping HWInfo64 running to see the temperatures.
The GPU acted normally, the only thing I noticed then was that the GPU Hot Spot Temp had a max of 94 degrees. From what I know, it should not be more than 90, but I thought that a thermal paste replacement should fix this problem. During the test I did not observe any other problems, no artefacts or problems with the fans, it seemed to work properly.

 

[Lutfij]

Welcome to the forums, newcomer!

I have a 850W Corsair RM850x 80+ Gold in my PC and I tried to change the cables but with no result.
How old is the unit?

I even tried to change the PSU with a Corsair RM550x 80+ Gold (550W)
How old is this unit?

Any idea of what went wrong with the GPU and possible fixes would be very appreciated.
When posting a thread of troubleshooting nature, it's customary to include your full system's specs. Please list the specs to your build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.

I even put the old GPU back and everything is normal, but with the 3060ti the PC just doesn't start.
The power draw difference between the GTX750Ti and the RTX3060Ti aren't the same.

 

[helx]

Welcome to the forums, newcomer!

I have a 850W Corsair RM850x 80+ Gold in my PC and I tried to change the cables but with no result.
How old is the unit?

I even tried to change the PSU with a Corsair RM550x 80+ Gold (550W)
How old is this unit?

Any idea of what went wrong with the GPU and possible fixes would be very appreciated.
When posting a thread of troubleshooting nature, it's customary to include your full system's specs. Please list the specs to your build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.

I even put the old GPU back and everything is normal, but with the 3060ti the PC just doesn't start.
The power draw difference between the GTX750Ti and the RTX3060Ti aren't the same.

Thanks for response. I updated my post, now including all the information.

 

[stonecarver]

At first, everything appeared to be working normal, I run some tests with Furmark and started to play some games.

I'm sure an oversight on my part but I didn't see where you did or did not DDU the 750ti driver before you put in new card.

 

[helx]

I'm sure an oversight on my part but I didn't see where you did or did not DDU the 750ti driver before you put in new card.

Yeah, I forgot to mention. I replaced the card before uninstalling the 750ti driver. After I boot up my PC, I went to the Geforce Experience and just saw that it wanted to install a new driver, which I did (express installation). After that I started to play the games and from here on I already stated what happened.