That night, Leo wrote on the Fonepad’s new system: “Don’t throw away old things. Learn to fix them. And always thank the people who share their knowledge online.”
ASUS locked the bootloader on later firmware updates. You need to unlock it via the official "ASUS Bootloader Unlock Tool" (APK). Note: This voids your warranty (irrelevant for a decade-old device) and wipes your data.
This comprehensive guide will walk you through the best custom ROMs available for the K004, the necessary preparations, and a step-by-step installation process.
If you are looking to restore the device to its original state or ensure it has the latest base software, you can find official firmware files on the ASUS Support site by searching for "K004" or "ME371MG".
Since the K004 is an older device, development has slowed down. However, there are still some legendary ROMs floating around the archives of XDA Developers that work flawlessly.