Mind you, the theory is applicable - but you may have issues seeing what is going on due to lumps of mechanism in the way. Could it be there's already a disc in the machine?
XXX
July 2016
Well you can take it to a place where they repair these things or you could take the lid off - power it up and insert a cassette and see why it's failing to load. The cassette is lowered - tape is pulled out and wound around the head and running gear.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix dvd players.