If you have installed firewalls then you must enter the details of the 2 PCs into the firewalls so it allows the 2 PCs to see each other.
I use ZoneAlarm firewall and I usually add the IP address of each PC to ZoneAlarm so that each PC can see the other.
These are the things below I usually check if I am having problems networking my PCs and sharing files:
1) Make sure each PC is in the same Windows Workgroup.
2) Make sure each PC has a folder that is shared.
3) Verify the IP address of each PC has not changed. They can change if you have multiple PCs connected to a router (can depend which one is turned on first)
4) Make sure the firewalls on each PC are set up to allow the other PC through using the correct IP address.
5) I also make sure each PC has a common userid and password registered (same on both PCs). May not be required but I usually do it.
After making any changes I also reboot both PCs to pick up the changes.
If you do all these things you can then go into networking and choose "View workgroup computers" and you should see the folders on the other PC.
To see if the firewall is blocking your connection you could turn the firewall OFF on each PC and then see if it works. If it DOES then you know you have to make some changes to the settings in the firewall.