Maximum PC

Hello. I have two PCs connecting over a switch. Oddly enough, one of the PC is unable to connect to the other. I've tried changing default gateways and IP addresses to no avail.
However, one of the PC's is able to connect to the other, but not vice-versa.

PC-A connects to PC-B (cmd ping) just fine. PC-B times out to PC-B (cmd ping).
The current configuration for the network is this.
IPv4 (PC-A) Address 192.168.6.2
IPv4 (PC-B) Address 192.168.6.4
DHCP Enabled: No
IPv4 Default Gateway 192.168.6.1
IPv4 DNS Server: 192.168.6.1
IPv4 WINS Server: 192.168.6.1
NetBIOS over Tcpip Enabled: Yes

PC-A runs Windows 7 and PC-B runs Windows Vista.

Any ideas on what might be the problem in this situation? Neither PC is running a firewall (aside from Windows). This connection used to work fine for months and after some absent time, randomly, no longer worked.

Thanks In Advance,
Houndf

How are you trying to connect?

My first guess would be Windows firewall, especially since you can connect one way but not the other. I've seen Windows update occasionally reset the settings back to the default deny everything.

Well I was doubtful, but that showed me. I disabled both of our OS firewalls and we were able to connect. I guess I was naive for excluding the OS firewall considering it hadn't caused any trouble in the past. Many thanks man!

Just to be specific the built in firewall will indeed block all ICMP coming to it.