Its never wise to flash the preloader.bin file found inside a ROM folder except we are really sure that the preloader.bin is exactly the one for that device. Since we are humans we are bound to always make mistakes hahahahaha you know were I'm actually getting at.
If you made a mistake and flash a ROM with a preloader.bin file which is not the one of the device, the preloader partition gets corrupted thus making the device not being detected by the PC, boot or even charge ie Dead Boot. Since it cannot be detected, there is no way you can reflash the phone even when the original ROM of the device is now available.
This post will show you how you can get your PC to be able to recognize the device again if its in such situation. This process to repair dead boots of mtk devices is known as Test Point.
Romkingz is not responsible for what ever may happen to your device after using this procedure
Do this at your own risk!
First you will have to loose the screws of the phone and take out the board.
Then on the board, you will find golden points with various labels like Tx, Rx, Vcc, KCOLO, COLO, KOLO, GND etc
Now locate a golden point with lable KCOLO or KOLO or COLO on the board. Sometimes these points are found at the volume terminal.
Solder a wire on that point (KCOLO, KOLO or COLO)
Locate the golden point with GND or normal ground on the board.
Join the wire form KCOLO or COLO or KOLO to GND on the board.
After joining this 2 points, connect the device to the PC and see if it detects.
If it doesn't, look for another golden point with same label till your device gets detected by PC.
When your device is detected by PC, it shows as MTK USB COM inside device manager.
Now you will have to quickly flash the original preloader.bin file or complete ROM.
After a successful flash process your device, you can now cut off the wire which you connected.
Couple back the phone & Reboot.
Points to note
Never use the Tx, Rx, Vcc or any other point that carry some amount of voltage
Hope this method works for you
Please if you have a working test point of a device kindly send the images so I can share to help others