I just reinstalled Yosemite 10.10.3 from scratch using another Mac onto the hard drive using target mode on the mac pro then copying the boot.efi file over to the two places it should be, but when the machines reboots and the apple logo comes and the loading bar it is crawling slowly up to 50% then stops.. I have tried installing a few times made a USB and downloaded yosemite again from the app store. I tried booting in verbose mode and it stops at every time at this:
Warning: couldn't block sleep during cache update
Warning: proceeding w/o DiskArb
/dev/disk0s2 on / (hfs, local, Journaled)
BootCacheControl: Unable to open /var/db/BootCache.playlist: 2 No such file or directory
bash: /etc/rc.server: No such file or directory
bash /etc/rc.installer_Cleanup: No such file or directory.
EDIT: Fixed it by downloading the pre patchet image on the front page