eMac Help needed urgently!!

Ok it is a emac 1GHz with 512MB of ram, and a Superdrive, and is 18 months old ish. There is a fault with this machine, and that is that the machine struggles to boot. Often the mac chime will sound but nothing will be displayed. I then pull the plug try again and again, and sometimes it rectifies itself after a few times, sometimes it won't.
Do you think it is soething loose inside or a common fault?
Thanks in advance
Alex

Try resetting the pmu. Disconnect all external devices and remove the memory access cover on the bottom of the eMac. There is a small round button near one end of the memory slots. The button is usually gray rubber on a square metal base. Push this ONCE and hold for a moment. Reassemble everything and try to boot. This will reset the PRAM also so you'll probably need to adjust mouse speed, date/time etc.

Hi, thanks for your advice.
I have now done this, but to no results. The problem still remains.
Any other ideas??!!
Alex

Have you tried the hardware test CD or system install DVD that came with these models? If it starts normally from one of these then it could be a system software problem. Run the hardware tests if it will start from the CD. Also, check the PRAM battery voltage while it's loaded. Disconnect the power cord so that the pmu is fed by the battery. Leave the battery in the cradle and check the voltage across it. The battery should read 3.5 volts.