OK, based on the new network cards also not working, maybe it could be a PCIe configuration issue? I would check the BIOS again, look for PCIe related stuff like speed or compatibility mode and stuff like that. There could be an OS-support setting too that could cause similar issues. Otherwise maybe some of the Chipset drivers are not correct? Those are annoying to troubleshoot, Windows should revert to default drivers if you delete the currently used driver trough device manager. Good luck!