DHCP ip addresses not show up in ARP list

Hi ALL!

There is an office where we use an RB2011iL as a router, it has a simple configuration.(dual wan, nat, DHCP server…) There are 10-12 computers in the office.The problem is that there is no internet on 3 computers (windows 7). They get an IP address from the DHCP server, but I can not ping the router from the computer. The problem is that the computers IP address + MAC is not in the arp list. But if I ping the computers IP address from the router the ip and Mac pair show up in the arp list and the internet works fine. I don’t no that the problem is in the RB or the computers could be have a virus or something.

thanks