Try this.
Go to the machine that port 445 is not working on.
Start -> Run -> CMD
In the CLI type "NETSH INT IP RESET LOG.TXT" <enter>
Should return you a CLI with NETSH>
Simply reboot the computer.
This will reset the entire TCP/IP stack on your machine to factory default. If there are any problems in the stack it will be rebuilt and should aut-correct itself.
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NOTE
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If you have a static IP address on 1 or several NICs in the machine, you will have to re--allocate them.
If you are using DHCP you should be fine.