I solved in this way.

Take your "Drivers & Utilities" DVD came with the notebook, look into the folder AFLASH2 and you will find the program AFLASH2.exe and your original bios file.
Also download the latest bios version for your notebook model from the "dowload" section of the official asus website.

Make a bootable dos cd-rom (you can easily use Nero Burning Rom too to do that) with those 3 files inside (aflash2.exe, original bios, latest bios).

Boot your notebook with this CD (if the bios doesnt want to boot from CD and insists in booting from HD only, you need to phisically remove your hard drive, it's very easy, and then you will be able to boot from CD).
Run AFLASH2.exe and flash the original bios.
Re-insert your hard drive.
Reboot.

You'll be able to enter in the BIOS settings again pressing F2 and without password.

Now, go into the bios "security" settings and SET A SUPERVISOR PASSWORD (for example, your name, so you want forget it). Save changes and exit from the bios.
Then, in the same way you flashed the original bios, reflash the latest bios version.
Reboot and press f2 to enter the bios. It will ask the password, just enter the one you set before.
Now you can remove the supervisor password (if you prefer) just going to change it and pressing Enter without typing anything. Save changes and exit.

Enjoy.

look into the folder AFLASH2 and you will find the program AFLASH2.exe and your original bios file