(1) the kernel framebuffer video driver. Do you have bootsplash, usplash, splashy, etc for a graphical boot process? If so, you may need to disable it. Look in /boot/grub/menu.lst (if using grub) and look for vga=XXX where XXX is a number, change it to vga=normal or delete vga altogether. If vga isn't listed, look for "silent" or "verbose" and delete that to avoid using graphics during boot up.
(2) the video driver that xorg is using. In particular Nvidia drivers often cause that. The only way I have found to completely get rid of the blank screen problem is to not use the Nvidia drivers, but that means my TV-out functionality is gone I just load the nvidia driver when I want to watch a movie and use "nv" the rest of the time.