What sort of infection was it? I don't mind if you post the file name/path/detection in Russian. That's what Google translate is for.
I'm a bit lost, frankly. Try installing Avast again, if you're still keen, and under settings>updates>proxy settings check that you have "direct connection" selected.
I don't know how the Windows 7 firewall interface looks, nor what is possible with it, but if it's like a lot of other firewalls, maybe it contains Avast entries created as rules?
You could try altering these if possible, or deleting them after installing Avast, to see if it re-creates them correctly.