From: https://social.technet.microsoft.com/Forums/windowsserver/en-US/9a5a0536-80fe-40c8-93f2-fcd12607bb83/domain-pcs-syncing-incorrect-time?forum=winserverNIS

Hi Steve,
Thank you for the post.
The time Infrastructure are 
.Domain clients/server sync time from DC servers
.DC servers sync time from PDC server
.PDC server sync time from external time source
To show the local computer time source, run command 
"w32tm /query /source".
To configure PDC external time source , run command 
"w32tm /config /manualpeerlist:time.windows.com,0x01 /syncfromflags:manual /reliable:yes /update".
You could find other time server from http://www.pool.ntp.org/ to replace time.windows.com.
If there are more inquiries on this issue, please feel free to let us know.
Regards
Rick Tan
TechNet Community Support

From: https://social.technet.microsoft.com/Forums/windows/en-US/fd63a802-2168-4c6c-955a-f8311cac4330/windows-7-not-respond-to-ping?forum=w7itpronetworking

When you only stop the firewall service, it will cause the boot-time filters to load. 
The proper way to completely stop the firewall is by **setting the service to disabled** 
in Services Manager then stopping the service through one of the GUIs or Netsh. This 
behavior is by design. 
In Windows 7, you need to disable and stop the **"Base Filtering Engine" service** firstly.
Only stop the firewall service will put you in block mode. It could be the resean why 
you cannot ping the PC.
Microsoft doesn not recommend you stop the firewall service, only if you need to troubleshoot 
some issue. This behavior will increase the security risks. 
In addition, this blog would help you:
Stopping the Windows Authenticating Firewall Service and the boot time policy
http://blogs.technet.com/b/networking/archive/2009/03/24/stopping-the-windows-authenticating-firewall-service-and-the-boot-time-policy.aspx
Regards,
Miya

From: https://blogs.technet.microsoft.com/networking/2009/03/24/stopping-the-windows-authenticating-firewall-service-and-the-boot-time-policy/

Windows 7 and Windows Server 2008 R2
In Windows 7 and Windows Server 2008 R2, you first need to disable and stop the 
“Base Filtering Engine” service. Only stopping the Firewall service as described 
above will put you in block mode.