OK - I managed to get it to turn on, but it tries to go through the firmware update process again. Without the SD card, it says the SD card is missing. With it, it goes through the firmware update process again, and at the end it beeps, says it was successful, and then says to press any key to reboot. And then it goes back to the flashing screen.
If I can find my usb card reader, I can try reformatting the SD card. If I can't find the reader, what can I try next? thanks!