So it is still stuck on the Sprint screen? How did you do the hard resets? Try doing a hard reset by holding down BOTH softkeys and then poke the stylus in the reset hole at the same time. The screen should light up and ask you to confirm (press Y and/or spacebar). Then see what happens.
If not, see if you can put it in bootloader mode (hold down the power and voice record keys while pressing the stylus in the reset hole) and try to run the latest official Sprint ROM update (download it from
www.sprint.com/downloads/).
If that doesn't work you may have a hardware problem.