So, I screwed something up while unlocking market apps (not sure what yet, will figure that out in a bit), and the result was that my phone would do the splash screen and then would go to a blank screen. I still had an adb connection at that point (I'd enabled development earlier), but needed to reflash since I couldn't get a root prompt since the superuser app couldn't approve the request. Had to reflash to stock; note that I never got the phone/pc icon, I just had to force a reflash. Here's another "what worked for me":
What didn't work:
- Phone unplugged, putting battery in and holding down either both or the 'down' volume key + power. Phone would just keep cycling between black screen & at&t logo.
- Phone *plugged in*, putting battery in. You should see a large battery symbol showing that the phone is charging, but off. Then hold down both volume keys + power. Phone will cycle to black screen, then back to battery symbol, then black screen again.
- On that second or subsequent black screens, let go of the power key.
You should end up on the android shoveling "Downloading..." screen.
Now, on your desktop, if you're in windows either one of two things should have happened -- Odin should have seen the phone, saying "0:[COM6]" or something, or nothing happened.
If Odin saw your phone, hit start, and continue on your merry way.
If it did not, open up Device Manager. If you see an unknown "Gadget Serial" device, then you need to install the drivers for Samsung's serial download mode. These seem to be found in Samsung's PC Studio -- I installed "New PC Studio 1.4" (under Windows 7 x64, you have to tell it to install in compat mode for Vista). After that, unplug your phone and plug it back in and Odin should see it. Then continue with the download.
The first time you do this, it might just sit at "DO NOT TURN OFF TARGET". If it does for longer than a few seconds, unplug your phone, pull the battery, and start over. The second time, when it's actually working, you'll see messages about various files being downloaded, a blue progress bar will be on your phone.
Hope that helps.