I have never had a problem with my mac, but recently I was surfing the internet, and the screen seemed to freeze. I powered it off by holding the power button until it turned off, then tried to turn it back on. the apple screen came up, then the rotating wheel, then a grey progress bar at the bottom. The progress bar loads a few centimeters, then the whole thing just turns itself on. Someone advised popping out the memory and reinserting it, but that did not work. I have attached a link to a video of what it is doing, please let me know if anybody knows what could be wrong and how I could fix it.
https://dl.dropboxusercontent.com/u/15260662/iMac.mov
https://dl.dropboxusercontent.com/u/15260662/iMac.mov