Are you sure that your power supply is called "Master"? Is it a Cooler Master, perhaps? It's 800 watts? If so, what is the precise model of the Cooler Master?
What video card, if any, did you have install before the 560 Ti?
Are you running Windows 8? If so, can you log into the BIOS and check and verify that "secure boot" is disabled.
You stated that it doesn't power on? Do you mean the power supply or graphics card? How do you know it's not working? No image, no spinning PSU fan? Did you disable onboard video in the BIOS?