sounds like you are missing routing information. Each router, actually...each TCP/IP host on the network has a local routing table. For hosts to know where to send packets to, they have to have information in their local routing tables. In the case such as this...
RouterA <----> Router B <----> Router C
When you try to ping from router A through router B, router B needs to know where to send packets to if the destination in on the far side of router C. Router B can send packets to 2 different networks. Therefore, its routing table needs to have information about its interfaces as well as the two remote subnets (left of router A, and right of router C).
Here is a link to a tutorial that explains the process of routing on a LAN:
Thank you for the reply,yes i put the ip routing and i successfuly ping the computer in RouterA through computer in routerB, and Through routerB to RouterC i have no problem with,but the only problem is i cannot ping RouterA through the computer of RouterC.
If computer A can PING computer C, but C cannot PING A, then it doesnt appear to be a routing issue. This is because PING is a two-way process. When A pings C, the packets go from A to C and they have to come back from C to A. A routing issue would only allow packets to go one way, and not back.
Did you check computer A to make sure that the local firewall is not blocking incoming ICMP requests or that Computer C is not blocking outgoing ICMP requests?