Selling faulty devices and not exchanging them on return.

I purchased a new Data projector for my school on the 6th of April, as we use them in our classrooms. Barely 2 weeks later, the projector stops working, switching itself off and not coming back on again. Upon returning to the device to the store on the 20th of April, I am told that the machine must first be inspected, and depending on the problem the warranty may be voided. This should take 10-14 working days (keep in mind all the public holidays coming up). In the mean time, my classroom is left without a projector. What is the point of a warrantee if you are able to sell faulty devices and then basically blame the user because it stops working. Surely so soon after the device was purchased one should be able to exchange it. It would be obvious had it been dropped or damaged but that is not the case.

This was purchased as it is needed as part of the teaching process in the classroom. How do you take this broken projector back, with no replacement or refund while I must now make another plan for the classroom?