Graphics Cards not detected, rest of system runs fine

Icesterz

Prominent
Jul 1, 2017
5
0
510
Upgraded my Graphics Card which hasn't caused trouble for a month.

Once I booted the PC one day, though, neither the recent nor the old GPU could be detected.

iGPU works fine.
The entire system boots without problems, the only issue being that there's no detected GPU.

Two Monitors, Two VGA Cables and two PSUs have been tested to no avail for neither of the two GPUs.
Both GPUs are being powered, fans running.

Booting with 1 RAM stick didn't change anything.
Troubleshooting page got me nowhere.
Dust is not an issue.
BIOS priority is at PCIe -> PCI -> iGPU.
Reseating of the GPUs has happened often enough.

What is causing my PC to not detect my GPU anymore?

Specs:
MBO: ASUS M2N-VM/S
PSU: CORSAIR VS450, 450W
CPU: AMD Athlon 64x 4800+, 2x2.5GHz
RAM: 4x1GB DDR2
GPU: Original: GeForce 210
New : GeForce GTX 960 4GB
Monitor: 16:9 24" LG 24M45HQ-B
OS: Windows 7
 

Icesterz

Prominent
Jul 1, 2017
5
0
510
No.

With no secondary motherboard currently available to me, I won't be able to test that.
Thank you, though, a fault with the motherboard could be the issue.
I will attempt to find a motherboard to experiment on ASAP, although it might take a while.

Are there by chance any software issues that could have caused this?
I'm still unclear about how this coud just happen overnight.