So on the computer your having trouble with you CAN ping the gateway?
Can you ping www.yahoo.com?
If not try pinging 184.108.40.206...
If you can ping yahoo...Check firewalls, static ip address in tcp/ip.
Run virus, anit-spyware, hjt
Reduce the nic speet...right click my computer->properties->hardware->device manager->network adapters-> right click nic->properties->advanced tab->speed duplex->change value to 10 full duplex