I'd concurr with worn/weak/old/faulty laser.

Replace entire DVD mech (easy), or ask seller to give you your money back.

X5flyboy, my Mk3 was faulty so I replaced it with a Mk4. The Mk4 was secondhand and already had the mk4 software loaded on. The software is stored on the GPS/DVD/computer and by replacing the unit I automatically upgraded to mk4 software.

So the system I am running is now on Mk4 software but the drive will not read cd/dvd's so I can't use the navigation because the maps won't load. Hope this explains it.

Okay..., I still learning this stuff, but how do you know what's loaded in the Mk4? does it display the version? (4-????) Please forgive me if these appear to be too simple (dumb) questions. Am finally understanding MY nav (after owning it for 3yrs) and am just starting to update it from the original 3-1/20 version. I also am scheduled to install a Mk4 in a few weeks. So please forgive this "ol' dog" trying to learn new tricks.

Look on the top right corner of the settings screen

Yes, that part I've learned. I assume (something I really hate to do) when replacing a nav unit (Mk3 or Mk4) that the "new" unit has software already loaded?

If so, I understand it may need to have the software updated. I've learned (thanks to this website, and NOT from any dealers I've asked) that the latest version is V32, AND you also need V17 or a key CD to finish the install.

Only if purchased 2nd hand.
if purchased brand new from a dealer, it will not have the OS software loaded.

The latest version OS for the Mk4 is 4-1/100

This is available on OS disv v32 and on OS disc v31.
Remember, the OS disc contains software for 7 different nav computers

But generally, you always use the mosrt recent release OS disc (v32) to load the current software version(4-1/100) onto the nav.

The key CD is only needed for the Mk3 nav when changing from non-aplit screen to split-screen software versions.