Just for info if it helps anyone here. If you have a similar video card (8800GT) and get a black screen with booting the installer or Yosemite (in my case, only for the installer on my thumb drive), removing the following kext worked for me. Same trick in Mavericks. AppleTyMCEDriver.kextAppleUpstreamUserClient.kextApplePolicyControl.kext ( found in… System/Library/Extensions/AppleGraphicsControl.kext/Contents/PlugIns/ApplePolicyControl.kext) I Also removed any GeForce Tesla or NVD Tesla kext.
just to update and thank people in this thread for their time and help, the issue i had (not getting as far as the installer screen) was drivers.... solved here thanks to Rampage Dev. I probably have more to solve but making progress finally.
updated fine... only broke audio.
Replaced AppleHDA.kext. Restart/repair permissions, delete com.apple.kext.caches folder (I always forget to delete that) restart. Audio working.
Update: I'm getting KP's on initial boot up... dose not happen every time and after a hard shutdown and re-boot it's fine. Will try and take a picture next time it happens.