You can take most computers back to the way the Windows system was installed when it had its last installation but you wouldl lose all of your personal files and settings and that can be quite disruptive.
Can you plese tell us which version of Windows you're using and why you feel the need to take this action. Different versions of Windows work differently to go back to the way it was at installation. Also, someone could prrobably help you to fix any problems without doing that.
Warning note: You ask for somone to call you - please don't give out your telephone number to folks you don't know, or publish it here. That could lead to hundreds of junk calls.