first of all, make sure you picked the right driver manually. If you are sure that you are really sure but still not detecting, follow these steps
Shut down your computer and plug the monitor cables off
then, make sure your GPU is properly installed, then plug the monitor cable on to the graphics card. After, you should be able to boot normally, then try installing your drivers.
If still it doesn't recognize your card, try going to the motherboard BIOS and change graphics settings so that it'll use PCI-E only (should be available through the options), or try disabling integrated graphics (again should be available through the options).