I've had this issue twice since upgrading to 2.2.... Today was the first time since I had other issues... I found this strange since I just installed BossPrefs --- one of the apps I had issues with when upgrading to 2.2
I think the phone was on, just completely locked or something.. I also had an issue previously where it refused to turn on the backlight, but I could still see the screen and operate the phone via a flashlight....
I was able to get my phone to restart after holding both the lock and home buttons for almost 30-40 seconds..
Any ideas...... anyone?