if u've checked everything else (cables, connections etc.), then it's probably time to get the laser lens replaced.
the usable life of the cd laser lenses in the bmw cd changers are only about 5 years, depending on how often u use it. if u go to the dealer, they'll charge u a few hundred bucks and "fix" it for u. but, what they actually do is swap out the unit with another refurbed unit that's come back from the vendor. it's a rotating scheme they run- ie customers that bring in bad ones they send out to get serviced and replace the existing one with inventory coming back from the refurbishing vendor.
at the end of the day, you'll get a working unit. so, most customers don't care beyond that. if you're really stubborn about keeping your own unit, then you'll have to find a car audio shop that can service/ replace the lens for u.
for your reference, i've owned my car since 1998 and have changed the lens about 3 times already. (i drive a lot and listen a lot.) usually it's about $200 to change the lens including labor at the car repair place. the dealer charges $500+ depending where u go. so, pick your poison. a 3rd option is just to pick up a replacement unit from a 3rd party vendor like
www.bavarianautosport.com or what not. i'm not entirely sure, but someone once told me the $4 or $500 units they sell are all refurbs also, as new units typically cost twice that. (someone who knows might want to sound in on this.)
hope this helps.
p.s. try the "search" function on the site as this topic has been discussed many times over and over.
