Sounds like someone has been in it. You'll need suction cups to remove the screen. You can get them here: http://www.ifixit.com/Tools/Heavy-duty-Suction-Cups/IF145-023
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Here's how to do it: http://www.ifixit.com/Guide/Repair/Installing-iMac-Intel-27-Inch-Glass-Panel/1631/1
Sounds like someone has been in it. You'll need suction cups to remove the screen. You can get them here: http://www.ifixit.com/Tools/Heavy-duty-Suction-Cups/IF145-023