On certain NT servers, I have services running which seem to be poorly written and which have memory leaks. I have had such a server lock randomly - usually right after I have left for day or at 4am or (god forbid!) when I am eating lunch. The avoid the random lose of service, I schedule a reboot. I force a reboot of the server nightly (weekly, monthly or whatever period that makes sense) using AT scheduler to execute the resource kit utility shutdown.exe. The parameters for shutdown.exe are /l /r /y /c where /l local machine, /r reboot, /c close all programs and /y avoid having to say yes to questions. For example:

at 23:13 /every:M,T,W,Th,F shutdown /l /r /y /c

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