Back in May, I got my Mac Pro 1,1 to run 10.3 through using a Yosemite compatible Mac to install it onto the hard drive, then over writing the boot.efi file. It worked great and functioned fine. The hard drive was a 1.5TB so I partitioned space for Mac 10.6, Mac 10.10, and Free Space, splitting them up in 500 quantities. I didn't plan to use 10.6, but figured it could be useful to still keep around if things went to hell and didn't work as I don't have an install disk anymore. Since the graphics card that was shipped with the machine had to be removed due to compatibility issues, I replaced it with a EVGA GT 640. I installed Nvidia's most up-to-date web drivers when I installed the card. I had no issues with this configuration. I consulted this thread for information on performing this "software upgrade." http://forums.macrumors.com/threads/2006-2007-mac-pro-1-1-2-1-and-os-x-yosemite.1740775/ I installed OS X 10.10 Server and used it as a server for web, cacheing, vpn, file sharing, etc. In June 10.4 was released with a new version of Server. I installed 10.4 without issue, and the new version of server. Several of the buttons within server lost functionality, but I consider that an issue with OS X Server rather than the hardware. Most of it related to the web server not being able to use PHP. I'm booted into 10.10 all the time to use it as a server with the machine running 24/7/365. Yesterday, I installed the latest web drivers when I was prompted from a Nvidia Update screen. I went ahead and said yes and proceed with the install. When the Mac reboot, it came up in 10.6, rather than 10.10. I figured something got confused after the update. Therefore, I reinstalled the factory card from Apple in order to get a boot screen while I held down ALT to select 10.10, instead of 10.6. Following my selection of 10.10, OS X proceeds to boot to 10.6. No error message, no information - it just will not boot into 10.10. I had no issues before this update of the Nvidia web drivers. If I select 10.6, it boots in 10.6 like one would figure. Things I've tried: Repairing disk Permissions Repairing disk sudo cp boot.efi modified one of the one OS X uses in 10.10 Restarting the machine Attempting to start 10.10 in safe mode and single user mode (didn't work; only started 10.6 in both modes) Anybody have any idea what the web drivers graphics card update did to my Yosemite Install on a Mac Pro 1,1?