To check how long your computer has been on use the Task Manager. It so easy to use task manager, i hope everyone have been used it, if NO! then don’t worry i will guide you.
let’s me explain first what is Task Manager ?
Task Manager is tool where you can check which programs, services and processes are running currently on your computer.
To start Task Manager just right click of mouse on Window Task-bar.
Under the performance tab, there is one field labeled Up Time. You can See time here
Note: Have you any doubt, any problem? Your are free to ask me. just comment here.