well at last good news for me!!
I bought another identical mp4 and took a good backup of the new one
It has the latest -I think- firmware version (v321.5678 - 58,2mb uncompressed)..
Just now, I flashed my previous (with bad fw) mp4 with the new firmware and it is fixed 100% 8)
EDIT: well, 90% because the game emulator crashes -thats my only complain now!!
here it is uploaded:
http://rapidshare.com/files/140791876/PMPV321.5678.rar
EDIT: this fw is for board PMP-704-V23.00
From first look, this new fw has 10 languages, an upgrade function, better sound maybe more..?