Hi,
Unfortunately, it is not possible to replace the PCIe slot by itself. if you confirm that this is the faulty part, you will need to replace the entire motherboard.
before you are running to do so and probably buying a new computer in the process, double check that its the PCI-e slot. first, check the motherboard website/manual to make sure that the video card is supported by the motherboard and by the power supply as well. it might be insufficient resource to support that card. second, some more powerful video cards require additional power pins usually 6 or 8 aux power. perhaps you have not plugged these. last think Id do is try and find another computer that supports these cards 100% and try it on that to see if its working on another computer.
after all these, you can safely determine the issue.
Thanka