Bless tool unable to set current boot disk... now mac pro won't boot at all.

Hello, Recently my 2010 has been acting up. I currently have an Nvidia 970 running in my mac pro, and I dual boot Yosemite and Windows 8 via setting the start up disk in the system preferences whenever I needed. Each OS is on a separate HDD, so I have two in my computer. Everything has been working fine and stable for months now, but suddenly, I was not able to set the BOOTCAMP boot disk from the system preference, and started giving me this error “The bless tool was unable to set current boot disk”, I was able to restart and boot into mac though, so I googled the problem, and someone suggested that I try ALT+CMD+P+R on boot, so I did. But now my mac will not boot in any OS, I even took the Windows HDD Out of the computer, and I still cannot boot into mac. It will turn on, run for about 20 seconds, then shut off, and I do not know what to do!


Mind you, I have a non flashed card, so I cannot see the boot screen, and I have a black screen at boot until the login page comes up. But I still have the original GPU the mac came with, and I can put that back in so I can see whats happening at boot if I need to. Any help would be greatly appreciated!

Welcome to the Mac-Forums.

But I still have the original GPU the mac came with, and I can put that back in so I can see whats happening at boot if I need to. Any help would be greatly appreciated!

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Go ahead and do that. Then let us know what error you're receiving if any. One of our Mac Pro savvy members should be able to help you with the problem you're experiencing.