I have had my phone from the beginning but got the newer version due to my phone freezing up on me. Had received the OTA update and everything was good, still not fast enough. I have been watching how quick the rest of the vibrant's were and i said what the hell, let' root and apply the lag fix. i was impressed at just how smooth it was, should of came this way at a $500 price tag. i used the oneclick lag fix on the market, but had to use sdk to make it work. I said to myself "this work's great, i'ma install a rom" so i downloaded rom manager, i was checking out the setting's and it had a option to create a partition on the sd card for the roms, that's when it all went wrong, i got a solid black screen with only the hard buttons lighting up white, did some research, i could bring it back by going into download mode and flashing new software with ODIN, downloaded what i needed, downloaded 512 and uvj. It came back to life, so i searched around and found the new j16 update, went to ODIN to flash, could not get into download mode, tried everything, even t-mob tried helping me, surprising huh! then it happened, the little cell with the bright triangle then the cpu. tried everything i could find online, called t-mobile for help, had a very nice guy helping me out, i can see why they win customer service awards. My phone never came back. The kicker is the samsung vibrant is on back order, meaning they have to make me one. WTF, he tried to find a store to do a warranty replacement and no such luck, everyone is out in my area. so now i have to wait. I put in a claim with asurion to get a replacement, they'll let me know by tomorrow if they have it in their warehouse. This really sucks!!! i was so impressed with the lag fix. just made it what it should have been from the get go and my GPS was working.

 

so sorry, just sad had to go buy a beer to ease the pain. I tried that too and it still doesn't work.

 

I found this on XA
I have the same problem and the hardware button method isn't working and I am stuck at the Phone ! Computer screen, and I read around the forums and they say that some Vibrant's have the hardware method locked, so you can't boot into Download mode from using the buttons. Since adb cannot find the phone when its stuck at this screen it seems we are both screwed. I have found no other solution other than returning it Tmo, not sure if they will exchange since it might be a violation of warranty.
I have the new vibrant's that can't go into recovery with the button's and the computer won't recognize it. It really suck's

 

i wish i could try that, i don't know anyone with a vibrant. but my battery was at 75% when it happened, but it makes sense.

 

After trying several different methods, I believe that with the new phones the hardware buttons have been disabled, the reason why I had to use SDK. The phone is a completely beautiful paper weight. Thanks for the help, it seems there is no way to come back from this as I cant get my computer to recognize my phone so I can use ODIN. Hopefully they can make one fast enough, if not, I'ma complain to T-mo and try and get the a new phone or my money back, maybe nexus 2. You guy's know more than I do, what's gonna be the latest and greatest?