firewall settings

I have a network of two Win7 and one XP PCs. all using Norton 360 IS.  Networking is set up as best I can understand but I can not regularly talk PC-PC unless I first switch off firewalls (eg for 15 minutes).  After that, I can network properly for as long as I like - until I next switch off.  Sometimes (but only sometimes) if PCs have been on for several hours, they will connect without having to switch off firewalls.  I guess I could permanently switch off firewalls as I have a hardware firewall in router, but it seems nice to have them on and I SHOULD be able to set it up so that it will work properly.   Back a year or two ago everything worked, but not now.  Is it time I tried another product?

Gordon