Windows 10: Why has my valid activation key stopped working today?

My activation key has just stopped working and I now get an 'Acivate Windows' message in the bottom right corner. I have been using my activation key since I built my computer in August this year. When I bought the key I checked it with ShowKeyPlus: Edition: Win 10 RTM Professional Retail EULA: Retail I have tried to reactive it but get this message: Unable to activate Windows We can't activate Windows on this device because you don’t have a valid digital licence or product key. If you think you do have a valid licence or key, select Troubleshoot below. 0x803fa067My computer has not changed

:)

 

down arrow key stopped working

My razor lycosa down arrow key decided to not respond at some point today. The other ones work and so does the numpad arrow if i turn off the numlock. Sounds like its just broken and im screwed, but any suggestions?

 

Windows is not activated with valid product key

I bought this license and activated this Windows like 1 or 2 years ago, and it's a valid key, I had my Windows Activated and everything works perfectly until today when I saw a watermark at to bottom corner asking me to Activate Windows.

I tried to reenter my product key but it says that I do not have a valid product key and refuse to activate my windows

Is there any solution for this?

P.S. I didn't reinstall my Windows or make any hardware change

 

Activation key?

Today I downloaded the latest ESD file for Windows 10 (RTM version), and after installing it, it asks me for an activation key or I won't be able to personalize things.

I searched on google, and all the keys I've found don't work. One of them works but gives an error in the last step.

When I click 'Error details', it shows this: http://i.imgur.com/03eipgJ.png

How can I fix that, or what is the valid key?

Thanks!

Edit: Tried with different keys, whenever the key works, it gives that error in the last activation step.