I am using a GanzKlar DVD player with Divx.
I had that similar problem before. "No Disc" message when you insert any kind of disc, DVD, Audio CD etc.
I removed the cover of my unit and observed that the disc is spinning quite slowly.
Did some research and it suggested that the spindle motor might be the problem. Not necessarily the lens itself.
I removed the cd drive tray of my player and removed the spindle motor. (the motor which spins the disc) Its very easy to remove, just needed a soldering iron and a small screwdriver.
Went to Raon, and looked for a similar spindle motor, and luckily,they are very common and many stores sell them. The one I got cost only P100, brand new.
I soldered the new motor's wires, screwed it back to the drive tray, replaced the cd holder (don't push the cd holder too low, try pushing it a little bit at a time so the cd will have enough clearance fron the lens when its spinning).
Replaced the drive tray, reconnected the wires.
When I inserted a dvd, the disc spinned very fast and it read the dvd. I tried different kinds of cds with different contents, audio, divx, mp3. The unit read them all without any problems.