Help! Windows 8.1 suddenly needs activation again

[Robert]

Hello. First time posting here but I would really appreciate any help with this problem. So first the laptop I am having problems with is a Lenovo y50 that came with windows 8.1 pre-installed. Recently I have been having problems opening the pc setting app as it would immediately crash. This was not a big deal to me since I could still access settings from the control panel. However the bigger problem comes in that now I have an activation issue.

So all of a sudden my laptop, which has been running windows 8.1 for a few years now, says that windows is not activated and that I should go activate it. It shows the windows 8.1 build 9600 watermark on the right hand side. I cannot personalize anything and on the pc info it says windows is not activated even though it was for the past few years.

I went to cmd prompt to find the product key and even used a third party key finding software to find the value. But when I went to input the product key, Microsoft kept saying it it's not right.

I was worried this might mean I have a virus on the computer but I did a malware bytes scan and it found nothing. And I did a disk check scan and repair just the night before. I currently use this laptop mainly for playing games and browsing the internet, both which still works. I really don't want to do a clean restart on my laptop since I have a lot of files on here from over the years. However I am concerned that not activating windows will cause future problems. I would be grateful to anyone who could offer some help because this is really bugging me. Thank you in advance.

EDIT: I did a sfc/scan and a dism scan thanks to Fjeuber for recommending this but I got the fact that there r some corrupt files from the sfc scan. So I did a dism / online/ cleanup-image /rstore health, and I get error 0x800f081f. Not sure how to proceed from here.