Last news : I tried with another pc, and it works from time to time (meaning, the same dvd won't be seen once, or twice, then it will be recognized and will work)...I didn't try that with the notebook, i'll test tomorrow.
On my pc dvd reader, the dvds work all the time (though it's a 5 years old noname dvdrom !)
Edit : For instance the last dvd i tried : first try, nothing. second, nothing. third, recognized. fourth, nothing. fifth, recognized. sixth, nothing...
It can still write, i just tried. Problem is that it can't read the dvd it has just written (but the old dvd reader can). And i can't use my guarantee to exchange it as they ll see i installed 4166 firmware..damn