This happens to me on occasion. I'll be working on something and it just stops. Today it has been doing it when I switch from one model to another. SW seems to lock up and when I look at CPU usage all the cores are at something like 80% max. In most cases if I feel like waiting long enough it comes back. Sometime however it takes 5-10 minutes to finish whatever it's doing...which as far as I can tell is nothing.
This seems to happen not based on large files, complexity etc, just rather random. Today I was doing an FEA on simple part and had a small assy open, 100 parts or so. Did this several times. I waited a couple times and it came back to life after 3-4 minutes. the rest of the time I just killed SW and started over.