Follow these steps to update or reinstall the stock ROM on your Sanno i7 Plus:

Flashing a stock ROM can resolve persistent software issues such as boot loops, system hangs, or corrupted system files. For the , which is powered by the MediaTek MT6580 chipset, this process involves using the SP Flash Tool to write a new firmware image to the device's internal storage. Firmware Details for Sanno i7 Plus

If your phone doesn’t power on at all (except for a red LED blink when connected to a PC), the preloader is likely corrupted. Flashing can revive it.