Run diagnostics against your Active Directory domain.

If you don’t have the support tools installed, install them from your server
install disk.

Run dcdiag, netdiag and repadmin in verbose mode.
-> DCDIAG /V /C /D /E /s:yourdcname > c:dcdiag.log
-> netdiag.exe /v > c:netdiag.log (On each dc)
-> repadmin.exe /showrepl dc* /verbose /all /intersite > c:repl.txt
-> dnslint /ad /s "ip address of your dc"

Here are some other links:–pls-help-issues.aspx