Why can not I change the system time

There could be multiple reasons why you cant change the time. A lot of times its if your not the admin on the computer you dont have access to these functions. You may have deleted the program that runs this funstion - or part of the program. Also, if you look at the bottome right side of the screen there is a time click on that a lot of times you can change the time that way. If that doesnt work bring your computer back where you got it and they ca fix it for you.