Can't insert CD into drive
I cannot insert a CD into the drive slot of my 2011 iMac: it goes about half-way in and then hits a hard stop. There is no indication on the desktop or in any devices list of there being a mounted disc.
The eject button does nothing, nor does a restart with the eject button pressed.
I am not aware of having left a disc in there, and it would certainly not be a mini-disc as some correspondents have done. But how do I find out whether there is a disk in there, and if so how can I get it out?
Otherwise, what else can I try to attempt to bring the drive back to life?
Thanks.
iMac, OS X Yosemite (10.10.5), i7 2.8Ghz, 12 GB RAM