System Reboots at Login PLZ HELP

I have a NT Server that reboots 40 % of the time at the NT login Screen and 60 % of the time if you just leave it after you log in . Its not consistant but it always reboots in under 3 min but not always at a certin time (ex. not always at the 2 minmark.)I’m not sure what to do with it at this point I dont want to reinstall NT At this time the system is at a remote site and the staff their aren’t able to reinstall. any idea’s any files i could replace that might be causeing this problem?? Thanks in Advance