All of a sudden, when I turn on the computer, it seems to boot normal with the grey screen, the apple, and the spinning circle below the apple. It then just freezes .... I tried my snow leopard cd and it kernel panicked while trying to boot. I have Lion install on a USB drive and while booting it froze just like a regular boot. I have Windows 7 through Boot Camp and after choosing Windows, it was just a black screen. I have snow leopard or lion running on an external drive too and when choosing that, it just freezes too. Any ideas? Thanks in advance.