Cannot connect to any open port

I have a desktop computer that I haven't started for around half a year. Last week, when I started it, it made a lot of updates and later when I wanted to connect my laptop to it, it didn't work. This used to work in the past, so I started to debug the issue. I have Avast antivirus and the Windows Firewall enabled, I thought they might block something, so I disabled them, but still no luck. The ping works though and the desktop is able to connect to the internet (the browser works), but no incoming connections can be established. I don't think it is a router issue because not even my attempts to connect to the local ftp server installed on the desktop via 127.0.0.1 didn't work.
When I try to connect to the localhost on any port using putty I get a "Connection refused" network error.

Any ideas what can cause this?

Removing Avast did the trick, thanks a lot! Now I have to see why is Avast causing this problem in the first place.