I installed Yosemite, yes without a backup, but seeing as how I can't get to the recovery, internet recovery, or safeboot screens(or for that matter see a screen), I don't think that's the issue. I tried to reset the nv ram with cmd+option+p+r. That didn't work. I know it boots. I hear the harddrive running. I cannot use any external screen on hdmi or thunderbolt. All I see is a fully blank screen not even a mouse. I know I can get to terminal if anyone has any ideas to run on terminal.