Hello,
- What makes you believe that your Windows 10 PC has been hacked or that someone has accessed it without your permission?
- Have you noticed any unusual activity on your device, such as files being deleted or unknown software or applications being installed without your permission?
The first step is to disconnect your PC completely from the internet, including both Wi-Fi and Ethernet, and put your device in airplane mode.
Then, from another device, check your Microsoft Account Recent Activity page to see if there are any unusual activity:
https://account.live.com/Activity
If you notice any unusual activity in your account, expand the activity and select 'This wasn't me'. Microsoft will quickly block that unauthorized access, and you will be asked to secure your Microsoft account by adding a strong password for your account and enabling two-factor authentication.
How to help keep your Microsoft account secure
Once you have secured your account, run a full system scan using Microsoft Defender or reputable antivirus software, such as Malwarebytes, to check for viruses.
If you still believe the device may be compromised, back up all important files to a secure external drive. You can then perform a clean installation of Windows using bootable USB installation media.