[DOZ1T]

So there's many ways to break into a password protected Windows 10 computer, like moving cmd.exe to be accessed from the login screen and creating a new user, etc.

How can I completely prevent anyone from breaking into my computer and accessing any files?

[webdev77]

Prevent booting from other devices and use full disk encryption for best safety. You probably have nothing to actually worry about in all reality unless you plan on having your equipment seized.

[DOZ1T]

I suspect someone already wants to do this at my company, it's a personal computer but it's in the office overnight.

[VoIPv2]

So there's many ways to break into a password protected Windows 10 computer, like moving cmd.exe to be accessed from the login screen and creating a new user, etc.

How can I completely prevent anyone from breaking into my computer and accessing any files?

Enable Bios/UEFI password mode.
Disable bootup media USB, (Cd-Rom) if you have that on the computer, (FloppyDisk if you super old)
Enable encryption on your PC. (Bitlocker should be enabled by default on the computer)

If you run a very old computer. Pretty good indication a backdoor is on the BIOS and a default key can usually be entered to get into it. (Which bypasses the password)

[DOZ1T]

Oh thanks I didn't know I could add a password to BIOS!

[SIM-3717028]

Windows 10 is already broken into. Install gentoo.

For real, linux is much more secure. You can try system encryption with veracrypt but some say that it messes with windows update.

[VoIPv2]

Windows 10 is already broken into. Install gentoo.

For real, linux is much more secure. You can try system encryption with veracrypt but some say that it messes with windows update.

Linux is still vulnerable. Just less likely to be targeted or exploited.
CVE-2018-14634 & CVE-2018-17182 are two good examples of critical flaws for 2018. So that response is irrelevant to both the OP and to why Linux is "more secure". The only way to secure a desktop/laptop/computer is offline network access and with locked physical access.

Also @OP if you are afraid someone at your company is trying to attack your equipment that should be something you involve your HR in on with proof that shows this.