Hi, first off, have you fitted your new card to a PCI Express slot? assuming your mobo is pci express capable.
Secondly, you did not need to manually disabled the on-board graphics, the PC will automatically recognise that a new PCI Express card is fitted, and will disable the on-board graphics.
Also, in the bios you should reset the default graphics adaptor, change it to PCI-E, then save and exit.
Reboot and make sure you have the latest drivers.