Hi there, as for the iMac being unresponsive and dead, you can try to connect it to your functional iMac via an Ethernet cable and then start Target Disk Mode. By using this problematic iMac as an external hard drive, you may have a chance to access your files and folders.
Based on the condition that you have taken the HD out already, you're recommended to apply an available bare-drive adapter to the USB port on your new iMac for file accessing.
Last, it's always mentioned but I have to emphasize one more time here that you should back up your computer regularly since there are two kinds of drives, the one that has already fallen and the one that is going to fall.
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