Most time there should be warning events in the System event log, with a source called Time-Service.
To verify network connection and ntp settings you can use w32tm.
show source server:
w32tm /query /source
verify network connectivity to an NTP server:
w32tm /stripchart /computer:ntp01.mydomain.zz
show configuration:
w32tm /query /configuration
(NT5DS using domain hierarchy)
force client to use domain hierarchy:
w32tm /config /syncfromflags:domhier /update
