I have a T-Mobile G1/HTC Dream, rooted, running CM6. It froze up at the lock screen, and after trying everything I popped the battery out and rebooted. However, this didn't solve the problem; I still couldn't get past the lock screen. After rebooting again (via battery removal, because nothing else worked), I only get a black screen (LCD on but blank). The problem seems different than other questions here on the site because I don't ever see the T-Mobile splash screen. I've tried Home+Power, Call+Menu+Power, Camera+Power, and none of those combos have allowed me to boot into recovery or factory reset, I still just see a black screen. When I plug in USB, the computer does not see the SD card.
Update: Now the LCD doesn't turn on either. Perhaps this is a problem with the ribbon after all? But that doesn't explain the freezing/booting issues.
Update: Although I only get a black screen, the phone does vibrate when I turn it on (using any of the key combinations mentioned above).