My computer shows nothing on screen

when I turn it on apart from saying "No boot device found, checking the device."What do I do?

This is saying that when it attempts to turn on, it cannot find a drive that has an internal operating system on it (Windows, Macintosh, Linux, etc.). I recommend using a flash drive on another computer and downloading a version of Windows/Linux to install on your hard drive. You can also attempt to open your computer and hook your SATA cable from your hard drive into a different port on your motherboard. If this does not work, you may attempt to try someone else's hard drive in your computer or your hard drive in someone else's computer to determine exactly what the problem is.

Copyrights goes to wikiHow

wikiHow Pro is intended only for your personal, non-commercial use

No boot device found應該關你隻SSD事（死硬件／揾唔到BOOT PARTITION）？

The solution is to reinstall OS. I made a mistake deleted the partition few years ago. So cannot boot. All data is lost.