Xbox displays System Error

Try to perform an offline update with USB stick using https://support.xbox.com/en-US/help/hardware-network/console/offline-system-update

If the offline update doesn’t work, replace the HDD. You should consider upgrading to 1gb or 2gb SDD. Before installing the HDD/SDD, you may have run script on your computer: https://gbatemp.net/threads/xbox-one-internal-hard-drive-upgrade-or-repair-build-any-size-drive-that-works-on-any-console.496212/

Does not power on

Open the Xbox and use Multimeter to test power supply. See this guide – https://youtu.be/x-njK1HL3gc?si=NlLXyMLUIQClzHkw . If the PS fails voltage test, then replace power supply and if still does not power on, then Xbox is likely dead or requires expert repair. IF the PS passes voltage test, Xbox is likely dead or requires expert repair.

No display, but powers on

Press and hold the console Power button and the Eject button until you hear a beep to turn on the console. You’ll hear one beep right away and a second beep 10 seconds later. The power light will flash on before the second beep. Don’t let go of buttons until you hear the second beep or see the console start up. See Xbox Support https://support.xbox.com/en-US/help/hardware-network/display-sound/tv-or-monitor-screen-is-blank-while-connected

Disc Drive System Error / Disc Drive not working

Open disc drive, desolder PCB, and solder PCB into replacement disc drive. See this guide https://www.ifixit.com/Guide/Xbox+One+Disc+Drive+PCB+Replacement/124453