You did give to little details. Doing IT on a computer is like doing the work of the mad dr. House as in the series of the same name.
The same symptoms can be from a million different diseases/conditions. And more often than not, you end up almost killing the patient if you want to cure him.
But thankfully as in the series, most of the time the patient survives and leaves with just a scare.
As long as one sees like that, it will be easier to remain calm.
I believe that your laptop, its OS and its data is probably ok. And it is just a misconfiguration of the boot. So be optimist.
My best advice would no doubt be for you to put the laptop in the hand of someone who has good experience with repairing them. Doing it online in this way is good only for those who are into S&M.
Note that there are many guys who “repair” and won’t care to try to “solve” the problem. 99% of the time, it will be easier to just reinstall the whole OS. Some don’t even try to backup the customer data.
Customers wouldn’t be able to pay the hours they would need to invest in really trying to find the root cause.
First here is an important note. If you ever feel the need to “invent” and personally format your laptop, then consider not doing it. Mostly because for many years now, most modern laptops have a hidden recovery partition on the system hard drive which is used to restore the system to factory settings in the event of system issues.
This basically means that your laptop has a hidden system that will do the formatting, OS installation and driver installation like it was when you purchased it. So no manual formatting as in the old days or you will probably loose all of that. The process is very simple and you should find It on the laptop manual. Or you can search for it on google. Note that the process is a little different depending on the laptop brand and model.
As for the symptoms “… the screen is black and the the system didn’t turn on…”, it can be many many things, even the graphic card as said earlier. The same thing happened to me when i was changing a graphic cards many years ago.
But in your case and reading the earlier comments, I don’t know how you did it (or if even if you did it. i am just randomly throwing ideas) but i would suspect that you managed to change the drive of the system boot in the Disk Management panel or something similar.
The “Disk Management” comment was about changing the drive letter of the external drive, not the system one…
The mentioned “Hiren’s BootCD” was a great tool used to help when “repairing” PCs, i don’t know if it is still used now? Many PC repair shops would swear by it. If you decide to use it then I would strongly recommend you to search for tutorials on youtube or similar to get to know how to use it and what to expect. It can be very confusing the first time.
And not only can it help you backup your data, it can also be used to check, restore, repair the problem and avoid the reinstallation of the OS. Etc.
Here is hoping for good news of the laptop.