Late 2012 iMac no longer boots. Black screen, no chime, no fans.

A family member of mine has a late 2012 27" iMac that crapped out maybe 2 months ago. I just got the chance to look at it the past few days and do my own diagnosis. It has an i7-3770 CPU, 8 GB memory, and the GTX 680MX GPU.

When pressing the power button, there is no chime and no audible fans spinning up. The display remains black, even after leaving it for hours on end. I can confirm the computer is receiving power.

What I have tried:

• NVRAM reset
• SMC reset
• Plugging the iMac into a different outlet in other parts of the house
• Disconnecting all peripherals except the power cable

This iMac has worked flawless since it's purchase on launch, with 2 exceptions:

• A few years ago, the internal 3 TB Seagate drive died. These models were notorious for failure. Unfortunately, it happened after Apple offered the replacement program. I ended up splitting the 3 TB fusion drive from the SSD and disabled the former.
• The Wi-Fi started having issues, maybe 6 months ago, staying connected. No changes have been made to the home's network, so this was a little odd. I ended up connecting it to Ethernet since it was right beside the router.

Any ideas or suggestions? I really don't want to take it apart with how much of a pain it is to do that, but I don't know what else I can do.

Thanks