If it's running on Linux, then edit ntp.conf to point to an ntp server. See
Clock Synchronization with NTP .
If it's running on Windows, then having Windows NTP client on won't help you; that thing is unreliable. (I don't know why, by the Windows 2003 servers at work don't keep proper time using the built-in Windows ntp client.) Instead, Google "Meinberg ntp client" and install that. Run the installer, follow all the defaults, point it to a nearby ntp server.
To find your local ntp server, either ask your ISP, who should be running one, or visit
NTPPoolServers < Servers < NTP and drill down to your location.
If it's running on OS X Server, then open System Preferences, click Date & Time, click Date & Time (yes, I meant that), check "Set date & time automatically" and use any ntp server, either your ISP's, one from the list I gave, or Apple's which is already in the list. (I've checked Apple's; it works.)