Asus rog don't display when power is turn on

Hello, i had a problem with my computer and it really depress me cause i had a lot of things to work on but suddenly when i open may laptop it say's "BOOTMGR is missing". I don't know what to do cause everytime I press ctrl + alt + delete keys button it keeps on repeating the process. I tried to fix it using youtube guides but unfortunately the display when i turn on my computer didn't appear. It was just all black display even when i felt that the fN of computer is wirking ang the power button Is working also. How do I fix this kind of problem. I barely need your help ASAP cause i have deadlines on the next following days and i had a rush on finishing it before deadline. I just hope that you can help me.