Vista - Can't ping any PC connected to my wireless modem

hi, I have two pcs under a wirelessrouter and a virtual machine in one of the pcs. I cant even ping the pc hosting the virtual one. If I ping the virtual machine from the host pc or other pc the result is: Reply from xxx.xxx.x.xx: Destination host unreachable. And if I try ping any PC from the virtual machine the result is: Requested timed out.
I was using comodo firewall and disabled it and the windows firewall too, as well as the anti virus. Any idea what can I do to so the machines can communicate?

Thanks

hi count, i just need to ask you a few questions, firstly, do you have UPnP enabled on your router/modem?

do you have networked devices with password protected sharing enabled? (right click network icon and select network and sharing center)

lastly, when you click on view computers and devices, does it come up with anything in there?

Thanks MrNeeds for your reply but I just found the problem.
In the wireless network connection properties window I uncheck the COMODO firewall and IPv6 boxes.

COMODO doesn't play well with Vista. Could have been the cause. Also, IPv6 is useless right now. So good thing to uncheck those.