Well, the firmware changing solved the problem.
And maybe the problem was caused by so many flashing in the first place
When I bought the drive the original firmware as B2K7, so I tried to install a 800A dual firmware but I got an error. So I tried the newest 800A firmware (B4N7) and I got another error and again no change was made to the firmware.
Then I tried the next version after B2K7 and installed sucessfully B2L7. I thought that I had to update each one of the firmwares till I reached the newest (I guessed it was different from another brands). So I did it: B2K7->B2L7->B2M7->B4N7->B3A7->B3C7-> B3D7 ->B5N7.
Afterwards, after posting in this forum I tried rolling56 suggestion and I went back to B3D7 and the "light problem" went away. Then I thought, what the hell lets crossflashed it and I installed B3EC. Then, I tried the latest B3KC and it made the upgrade.
Now I have the B3KC with the dual layer and so far so good. I read a dvd+r to test the speed and the performance is just the same as the older firmwares.
Well I never payed for a dual layer recorder and it seems that I have 2. Thanks to all the guys who made it possible