Hi,welcome to Seven Forums.
Make sure you all have the same default gateways,and that the prefered dns server ip address is the same on all the pc's.
Open your network and sharing settings, click on network and sharing,properties,choose ipv4,properties and make sure all the i.p's are entered correctly and match on the rest of the pc's(apart from the first one which is each pc's own i.p)
Not sure if this is the problem,hope it helps,and please reply with the results. Hope someone else can help you better