DNS server sudden change of network name

[kime8008]

Hello Everybody,

Can anyone help me solve this problem of mine, it has happen to my windows server 2008R2 twice now. I have just upgraded my server 2003 to server 2008R2 and install Active Directory, DHCP and DNS it was working fine I even created ADC server also running on 2008R2. the problem was from my PDC where I Installed the AD,DHCP and DNS I just rebooted my router and it automatically change my network name as example contoso.com was change to contoso.com2 can anyone please help me solve and give me the proper configuration to avoid this happening again

Thanks