Q:

"There are currently no logon servers to process the request" but 2 of 3 are still up

Both of the 2 DC's are running Svr 2012 R2 and are global catalogs. The DC that is down is our oldest one, SBS 2008. I have pointed DNS and DHCP at the 2x Svr 2012 R2 domain controllers. Also, both of the 2012 R2 DC's use themselves and each other for DNS, neither use the old SBS 08 DC. Yet, I still cannot logon while the SBS 08 DC is down (except for with cached credentials, which shows SBS 08 as %logonserver%). What could be the issue here? Thanks.  
EDIT: Also, I cannot open ADUC from any client PC's. Running DCDIAG on both of the 2 Svr2012R2 DC's, they both "failed test NetLogons" and " failed test Advertising" 
EDIT2: The NETLOGON folder does not exist on the old SBS '08 DC and I cannot figure out how to force it to get created. 

A:

Thanks, everyone. This is resolved now. The particular issue here was that the NETLOGON share was missing from the only working DC (SBS '08) in our domain. Once I created it and replicated out from the SBS 08 DC, all started working:
Windows SBS 08 domain controller is missing \\Localhost\NETLOGON share

