My network (largely Windows 7 machines) partly stopped working, from my laptop. Explorer would not browse to other machines, the network always showed empty. OTOH I could map drives by IP address and I could ping them cheerfully.
Other machines seemed unaffected - it was just me.
Hours of Googling got me nowhere.
Yesterday I just lucked onto it. On my laptop, the windows firewall thought my home network should be treated as public. Setting it back to a private network seems to have fixed all my woes.