Beeping and no solution

Good afternoon. I'm hoping someone here can give me a clue what I'm dealing with. I came back from half year in Asia in which time my iMac (27" mid 2010) was stored. When I try to start it up, I can hear the sound of the power supply and as soon the HD start to make the first faint sound, the iMac starts beeping. One continuous tone, same speed, same pause. I had this issue with an SD card of my camera inserted and also with the obvious issue, had RAM. I removed and played around with the ram in different slots, always with the same result. I can't find any corrosion in the RAM slots or on the RAM, which is what I had when it was beeping a few years back and I had to buy new RAM. I don't recall correctly if the background light of the display turns on when clicking the power button, or with delay at the moment of the starting sound and white screen, but I can't see any background light from the display when I turn it on. I also tried disconnecting the HD and without RAM but it's always the same result. I have to mention as well that I am in Puerto Rico and because there is still no electricity in my area in running on solar. Just to be sure it's not a lack of power for the power supply, I connected it to a generator but nothing happened. I couldn't hear the beeping because it was too load obviously. Any ideas how I can get my lovely iMac back to life? Could it be related to the HD? I wish I had a CD with the OSX to try that but I doubt I even get to the point to use option on the keyboard. Thank you!

I am confused. First you said

One continuous tone, same speed, same pause.

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but then you said

I couldn't hear the beeping

Click to expand...

So, was it beeping or one continuous tone. If continuous, what do you mean by "same speed, same pause?"

In any event, I strong suspect that it's related to both your dodgy power situation and/or a dead hard drive or power supply. Generators generally put out a square wave, not a true sine wave like a power company would have, so it might be that the power suppy in the iMac isn't responding well to that challenge. Ditto for solar sources, I believe.

At this point, if you give us a better understanding of the noise(s) you are hearing that might help someone diagnose it better than I have.

When I said I didn't hear anything it was because when I tested it with a generator of a neighbor it was too loud to make out the beeping but it didn't turn on either. I'm running a sine wave inverter rated for 500w continuous wattage.

Also when I said continuous beeping I mean on and off but not just 3 times as for RAM issues or with longer pauses in between or long or short tones. Same beep, same pause continuously.

What's interesting is that as soon I plug in the cable, still turned off, the inverter gives a warning sound as well, as if it drain too much power. I would have to turn off and on the inverter and then I can turn on the Mac. I also need to mention that the power supply isn't too old. I installed a new one one or two years back.

Still, it should have turned on on the generator then. I didn't had the chance to plug it in a regular outlet here yet. I would have to drive a bit to a friend etc.

If the harddrive was bad, which doesn't make much sense to me since it was just stored in one place, wouldn't disconnecting it, as I tried, turn on the screen white and show the question mark?

Thank you for the help!

I saw all possible pages already, which is why I'm writing here. I already checked the obvious.

We can speculate on the beeps, but until you can get that machine on regular AC power, trying to troubleshoot it is getting us nowhere. Drive to your friend's house that has AC power, plug it in and note what it's doing and then report back to us if the problem persists.