There are a lot of reasons why a computer would freeze. But more often than not the freeze indicates that the resources being utilized pegs either the processor/CPU, network, or disk meaning that it takes the amount to 100%. It usually means there is one or more programs/browser extensions running that is not behaving very well. You can start with programs that are running in the background and and slim them down, stop a bunch of auto-start programs, shut off unused services, remove bad add-ons and extensions from the browser and a lot of this would go away.

As for a free program to do this... well you get what you pay for...