If the system refuses to power on, its usually a power short of some kind. Double check the power connections going into the card and make sure they're not connected improperly. If you can, try and test with another PSU to will help confirm any auxiliary power connectors are not at fault.
If you remove the card from the system and it powers on, or the system works fine with another similar card please register your graphics card and file a support ticket at https://support.xfxproducts.com/ , in the ticket describe the issue in detail and also provide what troubleshooting steps you have taken.