Two servers on same datacenter cant ping each other

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http://serverfault.com – We got 2 CentOS servers on same datacenter. they both have websites using same mysql server. Most of the websites uses same source codes located on a.b.c.162. There is a shortcut to a.b.c.162 on a.b.c.164 placed on same location as a.b.c.162. So websites are reaching source codes through shoutcut between servers if website is located on a.b.c.164. System was working perfectly until this morning. But know servers can't ping each other but they can ping all the servers on same datacenter and i can ping them from my personal computer. Any ideas why it happened and how to solve this. Thanks (HowTos)