I was using hibernation in Windows Vista for about a year when it just finally disappeared. I don’t know what gives, but to renable it, goto command prompt and insert this
powercfg /hibernate on
Then reboot your machine and you will be all set

So how old is that server you have running? Does it need a refresh copy of Windows Server? You can check the date of install by running the following in a command window
 systeminfo | find /i “install date”