Administrative rights gone

[ON27]

Hello there, My friend is facing an issue with his laptop:

 

"i open the properties of my partition drive and in security by mistake i removed the tick mark of read and write of all groups so, i done that all again but i cannot open, rename and delete the files the files, it show you need administrator's permission i added that also but it doesn't work. I tried many times but it doesn't work so what should i do???"

Thanks!