Black screen, cooler and HDD turn off, tenant or dead?

Question

laptops

Good day to all!
I have a problem with an Acer Aspire V3-571G laptop (motherboard from this model). It all started with the fact that the motherboard on the Acer Aspire 5755G laptop failed, I didn’t bother with it and decided to buy a working one. There was no similar board available in online stores and I decided to purchase a fully compatible board of a newer model. It differs only in the cables of the matrix and the USB board on the right side of the laptop. I also purchased them, received the package, installed the cooling system, processor, RAM, connected the cables and decided to check. I connected the PSU, turned it on, the power and HDD indicators lit up, the cooler started spinning and after 2-3 seconds it stopped, the HDD indicator went out and the hard drive itself stopped rotating the disk after 20-30 seconds, there are no signs of life on the screen, even the backlight does not turn on. I decided to wait, after 2 minutes the cooler turned on, twisted and stopped again, but in general everything remained the same. Google suggested that the BIOS might have flown, decided to flash it, plugged the flash drive in, holding the FN + ESC keys pressed, turned on the laptop and no changes, everything repeated as described above, and the indicator on the flash drive does not light up and does not blink.
Tell me where to dig and what could be the reason?
PS There is no soldering station, oscilloscope and knowledge in this matter. I checked all the flutes, nothing fell off, I didn’t kill with static, I work in antistatic gloves and very carefully. I did cleaning laptops and replacing motherboards more than once, but this is the first time I encounter such a problem.

Answer 1

For the future, who had such a misfortune, there are several reasons:
1. A problem with RAM.
2. Problem with the processor.
3. Problem with BIOS.
4. Problem with discrete video system.
In my case, the fourth.