I am trying to clean up my sister's computer. She is running Windows 7. Program icons such as Mozilla Firefox disappear, Windows Defender won't turn on, and computer runs slowly. I ran Malwarebytes (had to install from a flash drive, it would not install from internet) -- it found 4500 PUPs. I also ran AdwCleaner, ESET online scanner, FRST, and Malwarebytes again. I tried to run RKill, but got the message "appdata doesn't exist."