Android Project Can't Suddenly Resolve Methods For No Reason

I made a simon says project at home and brought the disk on key to school, when I opened it on the program in the school computer all of this my code is solid and it works but for some reason all of these baisc methods like the R symbol that is used in "R.id.etc" the "AppCompatActivity" that is used in the title of the activity calss is not resolved and the app in

import android.support.v7.app.AppCompatActivity;

is not resloves , is there an easy fix for this issue? I have tried cleaning and rebuilding the project but my knowledge of this ide doesn't extend beyond that, my project builds with no erros but it shows errors for no reason on the code page and says it cannot resolve symbols. I have run the project on my phone and the build ran fine with no erros and the code worked just like before, my android final project is due in a week and I want to keep working on it please help .

i solved it by using this solution from a different thread posted by "Nauraushaun"

https://stackoverflow.com/a/30262226/7547488