Connect Windows 10 license to installed Windows 10

I recently bought a new desktop that came with Windows 7 Pro. After upgrading to Windows 10 and installing an SSD by partitioning the hard drive and making an image of the most important part, I have been using it for a few weeks with no trouble.

However, I just installed a GPU, and there were initially some troubles as I installed it, including the Blue Screen Of Death. After checking the Stop Code and finding instructions on this website to fix it by performing a check on the drive, I was able to make it work again, but since then the lower right corner of my screen has looked like

I checked Settings, and it said that I have error code 0xC004f034. I clicked the option to check my computer for a license, and the option that I had changed hardware recently, and it confirmed that I had a license for Windows 10 Pro on this machine that was running Windows 10 Pro... and said that I should now install Windows 10 Pro.

At first it looked like I could sidestep reinstalling everything if I just signed in to a Microsoft-affiliated account such as Skype, but I stopped pursuing that option when it became clear that I would then have a Microsoft account connected with this computer, and that my computer account password would be changed to that Microsoft password.

So, I'm now wondering if I can fix this problem of a watermark that tells me to activate Windows without being coerced to put a Microsoft account into Windows, spending money or reinstalling Windows.

Some specs about the Windows I have installed are:

As suggested, I ran ShowKeyPlus, and it shows an installed key as well as an original key.

From an elevated command prompt run the command: slmgr /upk

This will remove the product key from the system and allow you to enter a new product key.

Proceed to the activate windows screen again, and enter the Windows 7 product key from the original license you had. This should be located on an OEM sticker on the computer or with the the installation media you purchased.