not sure if you've solved this but...
my epic 4g tough is in the same mode and my pc wont detect it as a USB device
therefore i cant flash back to stock.
I learned from a tech guy at a cell shop near my house that if you put the stock tar file on an sd card and name it 'update.zip'
the phone will automatically recover using it.
Im preparing my sd card now and I'll post my results.