measure distance command does not work

I started to use AutoCad 2012 for student (my pc is windows vista business 32bit, service pack 2) .  And I had a hard time installing it. I am not sure it is because of that but every time I open AutoCad, I see the sign says " the drawing file eing opened was not created by a product from an Autodesk Education suite."  If you save this drawing, it will always be plotted with the follwing plot stamp: PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT it is recommended that you save this drawing with different file name.""

I don't really understand what this means.

I also have problem with using measure (distance). the line does not appear. My teacher said there should be. so, maybe broken?

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