How do you fix a Sony DVD player when it says 'cannot play disk' for every one you put in?

Basically how the question reads, my Sony DVD player won't play any disk and I have checked that the disk drive is clean and the disks are free off dust/scratches/dirt etc. I feel quite ill and want to watch a DVD to help me go to sleep but I also just want it to work anyway, how do I make it work?
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