How to fix blue screen of death windows 7 - [c000021a Fatal System Error]

#youtubeshorts So I tried using my old laptop. At first it worked fine with just minimal issues such as lagging and something like "powershell stopped running" during startup. I can&remember exactly what it was but the laptop was still operational. It is a Toshiba Satellite R850. Then, just recently, when I was watching youtube, it froze. Even control+alt+del won&work so I did force shut down because it was more than an hour that it didn&move. Now I have this problem. I just want to know if this can still be fixed without affecting my files. Because of the pandemic, I don&want to be going out unnecessarily and just be told that this is a hopeless case. I would really appreciate the response. Thanks in advance.