Doesn't boot at switch on ...

Hi to the Community,

hope this is the right place where to post my question :-) ...

I'm talking about an iMac 24" 2,16Ghz 1Gb 250Gb 8D BT AP - IC 4324A - BRCM1022 - EMC N° 2111

It is an older iMac with the same hump of the new ones but it is in a plastic transparent & white case.

This iMac has been donated to me by a friend of mine, his name is Pietro.

Pietro were asking to a 'specialist' to take care about his iMac and this 'specialist' where trying to change the OS on it ( this Pietro told me ).

Now this iMac doesn't work anymore and Pietro want to trown it away ... I have picked up immediately to try to repair it and use it in my house.

The problem is: " at switch on the screen light up and after a while ( 60 seconds or so ) it appear a small blinking world in the center of the screen and that's it".

It doesn't boot. I try than to switch it up while pressing CMD-R but same behavior as above.

Could someone help me in try to understand if there is something else I can try to understand the problem and try to recover it ?

Thank so much in advance to anyone willing to help me.

Best regards

Sergio.