DW1650 read just blank DVD/CD on dell computer

hi everyone,
I bought a Dell Computer (dimension 9150) about 6 month ago, it read all DVDs/CDs fine without any problem, but a day (september/october) it read nothing (at the time i doesn’t know it can read blank DVDs/CDs),so i wanna help from you guys, to get this problem off, please.
I opened the DVD-player one time to clean up the laser

when i bought it was a Philips DVD8801 then i flashed to BenQDW1650 BCHC (i thought flashing will resolve the problem but it didn’t)
If you wanna more info just tell it, i will do my best to find it

And by the way can plz someone tell me what a (write) book type is??thx^^