); Crystal ball is fritzed so best you give more info:

  1. What did you try, another firmware update? Which firmware?
  2. How? (i) In pre-boot as an RGN file, or (ii) still using GarminExpress but on another PC, or (iii) did you use the Asian 'Launcher' tool I linked?
  3. By 'still not powering on' do you mean that it still shows logo then powers off itself?

Unless we know EXACTLY what you've been trying and the clear results of that it becomes really hard to sensibly guide you further. You'll likely truly end up with a 'brick' (as in pretty paperweight) if these things are constantly flashed inappropriately.