Unexpected Shut Down

I'd start looking at hardware then. Check your RAM and make sure to check your fans.

My first guess (if you are sure it isn't software) would be heat or a bad stick of RAM.

If you don't have a RAM tester, you might want to spend the couple hundred bucks to invest in a good one. If you can't swing that, see if you can't get some new RAM to see if that is the error point.

thomson , you haven't mentioned any detail from the error logs or other logs . I assume there nothing important in the logs. Be careful for a repeating info log entry at boot up or just before shutdown . Possible causes can be :
1. server is receiving a software shutdown instruction from some app.
2.server is receiving a hardware shutdown instruction from some device.
For case 1 , check which app have shutdown instruction ability and check ....For case 2 check your NIC or Modem hardware whether it has wake on lan or dial in or shutdown features. Sometimes it goofs up in a way you explaned.
To me it looks up "NT Authority System ...shutting down error" of XP and old NY Server . The kernel is initiating the shutdown. Do the patches for the operating system supplied by your hardware vendor or microsoft . Some friends recommended to look at the RPC calls and in the services management menu "disable" or switch from "shut down on error" to another non-shutdown state in case an error is called . In short go into the running services and check which processes order a shutdown in case of an unexpected fault. and kill that entry to test ...

This could be the effect of many things.
here is a list of things i would look into fist.
close all ports and set up a fire wall with limited access or take server offline while doing this.

1. open regestry:
windows key + r brings up comand prompt
type regedt32, press enter
im not sure if the hive keys are the same for XP and server, but they should be simaler.
you will have a list of hive keys
do not delet or change anything.
brows the keys and look for anthing that looks suspisios.

under current config:
------sytem
----------current control set

most of these should be at default with nothing set under data value unless you have done something in the course of configuring the sever.
you should recognize these easily

2. open msconfig
type msconfig in the command prompt.
on the sixth tab over, anything that is a hk** may be important. cross cheack them with the registry and make sure they are not trojans / worms. disaable all that is not a legitamet hk** and restart computer. most of the rest of the list will be things like software and back ground programs.

3.bring up task manager and look at the prossess tab. anything suspisious: find its exe. file and scan for virus.

4. memory issue
i would not recomend running any version of server 2003 without 512 RAM.

***under:
system
-------advanced
------------performance
set vertual memory (page file) - minimum and maximum to 1.5x the amount of memory in your machine. this will help reduce fragmentaion of page file.

5. Defragment and sick clean up.
probably not a big deal, but it might help.

i hope this helps. im still only in my first year of college.

Really the past few days the server has been acting fine??!!!?? I checked the APC UPS and found that the unit must have been overloaded, because when I unplugged the monitor and our router, the system hasnt went down since. It says that I now have 31 mins of battery time, instead of 8.

Im not sure if this was the problem, but it may be a good start. The only thing I cant figure out is that I have the APC send me an email if it goes on battery power, or if its about to shut the server down. But I never got an email, it may have just been overloaded. Then again, this may not be the problem at all and the server is waiting for the worst possible time to shut down again.

Thanks for everyones suggestions!