Windows 10: Activation in windows 10 on a second hand PC

I have a second hand PC that already has windows installed on it and I'm getting an error message saying "you need to activate Windows before you can personalize your PC" I have tried to activate windows but there is no code that I am getting to activate my windows. we have had this PC for a year or so. What can I do?

:)

 

Windows 10 Tweaks

Pressing “Windows+Pause Break” (it’s up there next to scroll lock) opens the “System” Window.

Windows 10: In the new version of Windows, Explorer has a section called Quick Access. This includes your frequent folders and recent files. Explorer defaults to opening this page when you open a new window. If you’d rather open the usual This PC, with links to your drives and library folders, follow these steps:

• Open a new Explorer window.
• Click View in the ribbon.
• Click Options.
• Under General, next to “Open File Explorer to:” choose “This PC.”
• Click OK

credit to Lifehacker.

 

My PC suddenly says its not activated

I wish I could hands-on your PC .... it's a bit difficult explaining stuff...

 

Second Hand PC

I recently purchased a computer second hand, to which it worked perfectly in his home. To when I got home, I was hit with Activate Windows.

So using my old Windows 10 activation code from my old pc, I am hit with

"We can't activate windows on this device as we can't connect to your organization's activation server. Make sure you're connected to your organization's network and try again. If you continue having problems with activation, contact your organization's
support person. Error code: 0x8007007B.

Said person who I bought the computer off of was moving house, and I got a new phone the same day and have no way to contact him due to old phone being restored. I have tried multiple idea's from community posts similar to mine and none have worked. If anyone
could help that would be great, thankyou.