I changed my user account name and now my laptop is unable to boot up.

Well there are two administrator accounts. One could be new. If there are passwords hints. Your only choice is that if this computer does boot up. That is if both the administrators are allowed to male changes to the computer. And please. Delete the accounts in the Control Panel at the most cases. This type of issue is very daunting. This would not happen through the Control Panel. In any case check some of the replies here and in the other forums regarding fresh installs and all. It's not worth the trouble. And you should really find out if that windows is even active. Maybe that's what's causing the problem.

Okay. I am kind of on a more sustainable memory now.

Considering I am everything John, Andrew and Guest.

And the course here is that it's Lenovo to blame. You did not actually delete any user files. 

What you have to do is attach the hard disk to an enclosure or a SATA to usb disk. 

You are going to have trouble here. Once you can enter the disk in any other console and look for the disk in your computer. Go to the disk properties. And go to the security panel and click on the advanced options. You will then be required to change the owner. The owner is in the advanced button tad. Use find in order to look for that user computer identities. And most likely use that computers already set up administrator user. From there you will have to check for user changes and the list will change to an addition s- type user profiles. Click on the users profiles and edit or add. Some option should allow you to change that user profile to the administrator on that computer. And that s- type profile should disappear and will be listed as the current administrator profile only. Click okay and wait for the changes. On some occasions not all the files in that folder will change and you can skip the ones that cue the problem. When the windows are closed the process is finished refresh the file explorer page to find the disk contents. Good luck, Pike.

If you upgraded to Win 10 when the free offer was made, you got a digital license that is linked to your Microsoft account. Ever see it at "START, Settings, Update & Security, Activation"...?...

Once you've got that, you need no Product ID ever again. You do need to be installing the same Edition (Home, Pro, etc.) that you had before, is all. But that is automatic. Just be sure to enter your Microsoft account password during the installation process. Here are my tips on the process...

(1) Definitely backup your user files & downloads first because they get wiped in a clean install. I would even say to make a Windows system image backup first (which could restore the computer to its current state), except its current state is pitiful.

(2) If you give it your Microsoft account password when asked, Windows will be activated by the end of the install process. Also, reconnecting to OneDrive, your email account, the Store, etc., is all automatic. Some Windows settings held on OneDrive will be restored & any files you've put there will be accessible. Nevertheless, I would first back those up to external media as well.

(3) The only other password I was asked for was my WiFi password (written on the router). WiFi was automatically all set up afterward. But I did have to reinstall my WiFi printer.

(4) BIOS & other firmware won't be affected by the clean install, but it's best to update them first.

(5) If the drive on which you choose to install Windows has a partition of your own you wish to keep, do not delete it. In that case, delete only the Windows partitions at the "Where do you want to install Windows" screen, & click "Next". I had no extras except two from Dell which I did delete.

(6) Only a few of my Dell/Intel/Realtek drivers needed to be updated afterward. Most just reappeared on their own fully updated. May as well have important ones handy, though, as Greg says in his article.

(7) It's best to do a UEFI install (not a Legacy install) for added security & the benefits of a GPT (not MBR) hard drive partitioning style. To do that, BIOS must be set for UEFI mode. If the computer is capable of it, it must have come that way from the factory. MSInfo32 (type into Search) shows it in BIOS Mode:  BIOS Mode UEFI. In addition, you must choose to boot the Installation media from the UEFI option (if more than one is offered), as Greg says.

It isn't going to be as tough as it sounds. Cortana began speaking after the first 18 minutes, & the installation was completed about 9 minutes later. Here is Greg's article...

https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_install/clean-install-windows-10/1c426bdf-79b1-4d42-be93-17378d93e587

Clean Install Windows 10

Yes I am going to reinstall windows, but don't know the product key. I searched on internet and find that it will automatically verifed my laptop because windows was already activated on my laptop. What do you think?