Protected Mode

I finally solved my problem with protected mode: the DWORDs in every descriptor was swapped!

Before, I had this:
CodeSel32 dd 00CF9A00h
dd 0000FFFFh

When it was supposed to be like this:
CodeSel32 dd 0000FFFFh
dd 00CF9A00h

I had a problem before that, the system descriptor bit was always off.

I hope this can help someone having the same troubles. ;-)