When I deactivate the firewall in Services I'm able to turn it on, but there's never been a problem like this before.
What set me on this path was that I'm having trouble getting homegroup to work. I've left the homegroup, deactivated HomeGroup Listener/Provider in Services and deleted the content of the PeerNetworking folder on each PC. This means that the homegroup is gone, so that when I activate HomeGroup Listener/Provider on one PC, it gives me the option of creating a new homegroup instead of joining one, right?
So 2 issues: firewall/file sharing and homegroup.
PC 1: created the homegroup.
PC 2: joined the homegroup. PC 1 and 2 have access to eachother.
PC 3: joined, but when I select to share all folders they are reverted to not shared. PC 1 and 2 can't see PC 3.
PC 4: joined and can leave, but it says that no other homegroup PC are available.
On PC 4 I get an error about note to node grouping, and that it can't connect to port 3587. It says that firewall and security policy settings are to blame. And then the next error says that the firewall is wrongly configured.