Well nothing should be changing the Admin password automatically.
The fact it is being changed automatically and it isn't you or the other techies, leaves me to beleive you have a virus doing this and is opening up your server to hacking.
you need to pull our server from the internaet and do extensive scanning for nasties.
Or worst case senario, as Tony says, start over again, what AV do you run? has nothing been picked up , is anything in quarantine?
What did the logs to the last scheduled full scan say?
"In complete darkness we are all the same, only our knowledge and wisdom separates us, don't let your eyes deceive you."
"If a shortcut was meant to be easy, it wouldn't be a shortcut, it would be the way!