(Doesn't work for Macs)
If you right mouse click on your desk top you will get a menu. Go to "properties" at the bottom of the list and click. Next click on the "screen saver" tab at the top of the list. Once there is a picture of a computer screen in that menu there should be a section at the bottom labeled power it will have a message next to the button that says something like this "To adjust monitor power settings and save energy. Click Power" So follow the directions and click on the power button. A new set of top tabs will appear at the top of the box. Click Hibernate and make sure the "enable hibernation" box is checked. Once this is confirmed, go back by clicking the "power schemes" tab and go through the drop down boxes and set all of the settings to "never" accept the "system hibernates after:___" and select how long you want to be able to leave the computer before it automatically hibernates.
If you click on the "advanced" tab at the top of the same window box, it will give you drop down menu selections for what you want the computer to do when you press the power button on the computer. Here you can select that you want it to go into hibernation and you are done.
It probably looks a lot more complicated than it is. You should have no problems doing this. You wont have access to these setting controls on the school computers though--unfortunately.
You should never loose information that is on the screen when the computer hibernates so there is nothing to worry about. The more it hibernates when you neglect it, the better it is for energy savings.