Offline after about 2 hours

I installed Hamachi (free) on 3 of my PC´s.
At my girlfriend's home and another.

Now I have the problem that everything works great for about 2 hours, but then the "unused" 
computers "gray" go offline.

I checked the energy settings and deactivated everything, so it can't be because of that.
But how do I solve my problem?
I want the invoice to always be active at Hamachi and to be able to access it at any time.