I know its a joke, but cutting PFF power is never a good idea. It makes any kind of forensics a lot harder, and its probably not going to help anyway. You should isolate the computer from the network, and then call a professional.
However, putting the computer to sleep/hibernate it may help, just so I.e ransomware can't continue encrypting, but maybe still has keys in memory, if you're lucky. This is only my theory, though, not sire what are the best practices.