hmmm....i was having a problem today where my g1 just died on me and when tryin to switch on, the tmobile and android screen would appear but then just remain blank. Only way i found around it was by doing a system restore.
to do a restore (u will lose any data and apps on the g1) turn off the phone then:
hold the Home key and the End key for about 20 seconds, or until you see a “triangle with an exclamation point and a picture of the G1″ on the display.
then open up the QWERTY keyboard and hit “Alt+W” and it will then be restored to factory settings.