Hi
To answer the question about virus hiding in system RAM. While a machine is running, yes. But once shut down, no. You do have nightmares like root kits, virus hiding outside allocated disk space, CMOS, BIOS and other exotic stuff. Some more imagined than real (and some very, very real). Some malware likes to hide on USB sticks. Some hide inside pictures or video! Remember a picture is just code, and within that code can be malware.
After an infection observe the machine carefully and check out its operation. Look carefully for any suspicious behavior. For complicated malware run any programs you can get your hands on against it. You will be surprised that the third time you run the fifth program you have tried, BINGO, it will find some more malware. this is one reason that it takes time to find and kill this stuff. Pros have better intuition and maybe have seen it before. Pros can work faster with better results. But it is the same for everyone. Look for symptoms and then cures.
Thank you again to everyone. Lots of smart. helpful people on this site.
I am getting ready to physically swap out my c: drive after many scans to an older backup. Since my media drives have photos and video that weren't encrypted I am still concerned (after clean scans) about something hiding there.