It sounds like unit is cycling through each cd holder, loading the respective CD and then looking for the first track or index on the CD. Most changers cycle through the magazine like this, and they know if they've found a CD when it can read the first index on the CD. If it can not read anything, then it assumes the tray was empty and proceeds to the next tray (looking for a CD, and so on).
In your case, it sounds like the changer is loading the CD, tries to read the first index, doesn't read anything and proceeds to the next CD. It could be an alignment problem (laser isn't tracking properly), a dirty lens, but I'm still leaning towards the laser being burned out.
If it's an alignment issue, usually the changer will try & try to read the CD and you can hear some high pitched digital type noise coming from the changer - you have to listen very, very closely to the changer unit. Most integrated changers report back "ERR" on the head unit display if this happens.
If it's a dirty lens, problems are usually intermittant and it doesn't happen all at once. Dust builds over time, condensation helps to bond the dust to the laser, etc. If this has been happening over time and getting progressively worse, it could be just dirty optics/laser.
If the problem started all at once - think of it as a light bulb burning out. 3 to 5 years was the normal life span of a CD laser in the early to mid '90s.