Intel iMac won't boot. Starting chime, then beeping. What's wrong with it?

I pressed the power button on my iMac to turn it on - I didn't hold the button down, it was just a normal press - and it made the normal start up chime when turned on, but after that it beeps twice, then after that it beeps three times every three seconds and won't start up. I pressed the power button and tried again, but still the same thing. I tried holding down the power button to power on to do whatever that does (I can't remember exactly). It makes the long beep sound, makes the start up chime, then the same thing. I'm not sure what to do. I've have some very important files and projects that I can't afford to lose... sigh Can someone tell me what to do?

Message was edited by: digitalhigh