I have a macpro1,1 that was running snow leopard. Something needed Lion (the latest version of osx that will run on this mac pro), so I installed Lion on another set of disks. All was going well until I installed BOINC. After the restart (which is annoying to require in the first place), after the apple logo appears, a circle with a slash appears and that's as far as it gets. I had to revert to the snow leopard disks to get it to boot. What do I need to undo to get Lion back? Thanks...