I found this but I cannot attest to knowing anything about the supplier. Hopefully this will help guide you towards the part you’re looking for. http://www.notebookparts.com/new-genuine-lenovo-yoga-720-13ikb-lcd-back-cover-am1yj000200/?gclid=Cj0KCQiA14TjBRD_ARIsA...
here's a link to a similar issue that you are experiencing. The solved answer should provide you with the answer to your issue! If not, let me know and I can try to further assist.No picture but there is sound
This could be a simple corruption in the Operating System and a Reinstall of Windows could fix it, it could also be a failing hard drive. If you are not sure how to create a bootable drive that could be used to test the drive, I would recommend having it tested at a local computer repair shop. I personally use Medicat to boot into a PC in order to test the hard drive. https://gbatemp.net/threads/medicat-dvd-a-multiboot-linux-dvd.361577/
Do you know where to buy a replacement battery for this device?