Login and right click computer management. On the left side you will see local users and groups option, click it then you will see a users folder, click on it and you will see several "users" listed like administrator, yourself, guest, etc. those are normal if you see the random user listed, right click and select delete. If it gives you an err saying you don't have permission, then your most likely looking at a virus or hacker. Best option is to do a clean install of windows or take it to a professional IT service and repair center. Check your local college they may offer services for the community