IMac G5 (Intel): shut down, and won't turn on

Question

I've had my iMac now for well over a month now, I'd say about 2 months, and after the first week I removed the default memory stick that came with it, and installed 4 GB (2x2). The computer has been running fine with the new memory for over a month, so I'm pretty sure the memory is not an issue, the computer itself has been working perfect up until tonight.
So I was doing my normal web surfing, and little bit of graphics editing when out of nowhere the iMac just shut down, like it went from a regular screen to just black screen. I then proceeded by hitting the power button, and got nothing. Held the power button down for 15-20 seconds, then hit the power button once again holding for 2-3 seconds. Now I hear the hard drive sound, like it's starting up the hard drive, but I never hear the Apple "aaahhhh" sound, nor does my screen even turn on. It would seem as if it just dies from there but it's obviously not, because if I goto tap the power button again for 2-3 seconds it won't make the same noise the hard drive makes when it's turned on. But if I hold the power button down again for 15-20 seconds, then proceed by tapping the power button again afterwards I can hear the hard drive sound like it starts up again, but still no screen no Apple sound.
*Failed Fixes Tried:*
- removed memory and reinserted memory.
- remove power cord for 30 seconds, plug back in, start up.
- make sure the power cord is plugged in to an outlet with power (I more than obviously think it is receiving power due to the hard drive sound starting up, but maybe the computer is not being fed enough voltage which is why it's not starting up? Then again it's still odd because I've been using it like this fine for months.

Answer 1

Take it in for service.