By default on Windows systems, hibernate is enabled. This includes servers, which should probably never enter hibernate state. The problem with hibernate, especially on older servers, is that the system reserves hard disk space large enough to store the contents of the RAM in the C:\hiberfil.sys file, which is a protected system file. If you have a small hard drive and a bunch of RAM, this can very quickly eat up a lot of valuable disk space. The only way to get this space back is to disable hibernate, which in most cases for servers, is a best practice anyway.
The easiest way to disable hibernate is to open a command prompt (cmd.exe) as administrator and run this command:
powercfg.exe -H off