Question : My iMac wont start

I was using my iMac, it was running really slow, so i decided to restart it and it froze up. I was forced to shut it down manually by holding the button. When i went to turn it back on, it made an unusual beep sound and then said somethign along the lines of "you need to restart hold down the power button for several seconds or press the restart button". it just does this over and over again. i have turned the power off at the wall for 20 seoconds and its still doing it.

Answer : My iMac wont start

Ok, if you'll replacing RAM, please check DDR2 frequency. For example, old MacBookPro 15-17"  does not startup with DDR2 800.