811s fails to read empty dvd-r's

My 811s drive has always worked fine, I’ve burnt about 40 dvd-r’s (Traxdata 4x RitekG04)without problem.
Suddenly I had difficulties reading empty dvd-r’s.
First the drive read dvd-r half of the time, later only after i rebooted and first inserted a normal dvd, but now it refuses empty dvd-r.
When I insert a blank disc, the green light flickers and the drive
makes weird sounds for about 2 minutes. Then it stops and when I
try to burn with Nero it says ‘no disc’.
I can still read/burn all other formats (also dvd-rw).
This didn’t happen after a firmwre change, it happened at a random day.
I tried to flash to older/newer/patched firmwares but same problem.
First I thought it may be the dvd-r’s itself (last 10 of spindel bad quality maybe),so I bought a new spindel Traxdata 4x RitekG04 and also dvd-r’s from Ritek (purple, RitekG04), but no luck

Any ideas?

Faulty drive?