I set this up last night. I have an issue. I wanted to set up my external Samsung SSD drive as my boot drive and use the internal drive for data. The problem when I reboot, I get a signal loss and it powers down into energy saving mode. I hit the button on the monitor and it boots me to the log-in. I tried to use the alt key to install Yosemite on the external but it won't give me that option. I'm connected through Thunderbolt. Any tips on how to do this?