why is my optical drive is NOT accepting ANY discs, including the start-up disc?

i noticed that other Mac users are having the same problem with the optical drive. why does Apple keep using another company's inferior products in their own products when it makes Apple look bad? i also tried my Apple external drive and the iMac won't even read that either.

and another question: why is it that when i typed my iMac's serial number, the Apple website couldn't locate/identify my iMac? the website then assumes that the user cannot find their own serial number, which is condescending.