Answers (1)
"""Windows automatically resets your computer's uptime -- the total number of hours that your computer has been running since its last reboot -- each time you restart the machine. This means that although you cannot track the total number of hours your computer has been running since it was first powered on, you can still determine how long it has been running since its last reboot."""
Cmd -> "systeminfo" -> System boot time.
A date on bios may provide a rough estimate. Or run a script / tool to list & sort the creation / modification date of every file in storage (not all methods of file creation comply with this, however, so may have to cull some values).