Has there been any hardware changes recently? Have you tried to activate again via phone? Sometimes, when the internet one won't work, try the phone activation. You'll have to punch in or read a lot of numbers, etc. But many times it works. You can quickly get to it at a CMD prompt and type: SLUI 4 and follow the prompts.
Also, if you run slmgr /dlv at a CMD prompt, what does the DESCRIPTION say in the pop-up results? Is it retail, OEM, Volume_KMSChannel, etc?
Depending on what it is, you might have to re-enter your Product Key, etc. Here is an article RE: SLMGR where you can set your product key if needed and register with that newly set product key.