Will not install from dvd

My Intel iMac bought in 2011 suddenly crashed and now will not restart. I get a grey screen with the apple logo with a whirly which is as far as it gets. I have tried holding down the shift key on startup but that eventually takes me to a blank blue screen. I tried resetting the pram to no avail. I tried the unplugging for 15 seconds also to no avail. I then tried loading the install OS 10.6 DVD but the screen goes blank and then there are 3 hoots, like a boing, which repeat regularly every few seconds. Oh, I also tried removing and pushing back the ram chips in case there was a loose connection. I have / had tried disconnecting all peripherals including with and without the usb keyboard and mouse

Poor me, the machine is exactly 6 weeks out of warranty!

Can anyone help or seen this before?