Why my phone can't display anything

It sounds like a screen-related failure. I'd first try to take it apart and disconnect and reconnect as many wires as you can disconnect from it without soldering (which may or may not be all of them depending on what sort of phone this is), and test it again. If that doesn't work, you'll probably have to replace the screen. I'd send a guide, but I have no idea which phone this is, and it doesn't look like there's a page on this site for it, so results are... unlikely at best. Good luck! And do send updates!

If your phone can’t display anything, the most common reasons are battery, screen, or software issues. The battery may be completely drained or faulty, preventing the phone from powering on. A damaged display or loose screen connector can cause a black screen even if the phone is running. Software problems, such as a crashed system update or corrupted firmware, may also stop the display from loading. In some cases, the phone is on but the brightness is set too low or the device is stuck in sleep mode. If charging and restarting don’t help, professional repair may be needed.