Thanks for the responses, guys. Had already tried the battery removal and soft resets with no luck.
lightbiter, thanks for the reminder about getting into the bootloader -- I had forgotten it was possible to do that. Unfortunately, that's not doing the trick for me either. When I try to re-flash my official Sprint ROM, the progress bar never gets past 0%, the device reboots, the process fails, and I get the following error message:
This has happened each time across three attempts now -- any ideas what I may be doing wrong?
Palm Treo 800w: RealVGA @ 96dpi, WeatherPanel with PhatPhinger 320, phoneAlarm Pro, UltimateLaunch, Conduits Pocket Player, Opera Mini, and IM+.