[Tutorial] How to fix preloader detection error on a Mediatek Android phone

[hovatek]

Ideally, Device Manager should refresh and detect your Mediatek (MTK) Android phone when you connect the phone to PC (while switched off & with a charged battery in it).
In the case of a preloader detection error, Device Manager will only refresh when the phone is connected while switched on. The phone's MTP and USB connection would also work fine (i.e the PC will detect, read & write to the internal storage / SD card storage) so that rules out a USB cord / Port issue.
It is important to note that in this case, even installing VCOM drivers like @ https://forum.hovatek.com/thread-440.html still doesn't make Device Manager detect the phone while switched off.  

Cause

You might encounter this error after installing a custom ROM and are trying to revert to stock ROM using SP flash tool or any scatter format flashing tool. The phone would consistently show a charging sign during flashing attempts

How to fix preloader detection issues

To fix a preloader detection issue, take out and reinsert the battery. If the battery is inbuilt or taking out the battery doesn't help, setup ADB-Fatboot using https://forum.hovatek.com/thread-588.html
Launch ADB and run the following commands

Code:

adb devices
adb reboot-bootloader

Once the phone enters fastboot, the drivers should start getting installed; do not interrupt.