RE: POST failed when plug in PCI-E 8X network adapter
PCI-e 2.0 cards are not compatible. PCI-E 2.1 and 3.0 are required. The 7050 does not have any slots designed to work as you are trying. X16 slots are for non SLI non Crossfire Video not for PCI-E 2.0 nics.
The 7810 works because there are
PCIe x16 slot (PCIe 2.0 wired as x4) (slot 5)
The 7050 is not a server and not designed to be a server or high end workstation.
PCI-E 3.0 is not backwards compatible with 2.0 or 1.0 due to power as well as bus speed and Line Code it is with 2.1.
8b/10b is a line code that maps 8-bit words to 10-bit symbols to achieve DC-balance and bounded disparity, and yet provide enough state changes to allow reasonable clock speed recovery.
128b/130b encoding in PCI-Express Gen3 and up is not backwards compatible at the BIOS level.