after upgrading gutsy 18-12-07 my local network is not working

[david]

after upgrading gutsy 18-12-07 my local network is not working

I am using a ubuntu gutsy (the 64 bit version) which I updated yesterday
using the update program. All seemed to go well until I rebooted and
found the pc's would not talk to each other.
I can ping the router with both pc's but not each other
I then installed guarddog and enabled (opened) every thing still no
good.
So I disabled the guarddog with its check box, still no good
I would apprecite any help

Dave