New iMac, old one was defect

I got my new iMac last thursday!! yeahhhh..
this was my Christmas gift but the one I got was defect. Every once in a while, it was shutting down and I needed to unplug it, wait a while to get it back working again. Since it was bought at FutureShop, I had no problem exchanging it for another one. Will post a picture soon..

Spec:

24″ inch iMac
2.8ghz
4g ram