Twice today I closed my computer (putting it to sleep) and when I opened it back up it wouldn't turn on at all. It was completely unresponsive but would eventually turn on after about 15 minutes. Now I shut it again and it won't turn back on at all, and it's been over an hour. I have an appointment with the Genius Bar tomorrow, but does anyone know of any troubleshooting tips that could get my computer working long enough for me to back up everything?