iMac alive but dead...

I've got this old iMac that I'm trying to get up and running again. When I hit the power button, the fans kick in and I can hear those classic iMac mechanical sounds. The only hitch is that it seems to stay in that state forever. No startup chime, just a black screen.
After opening up the iMac whent to take a look at the the diagnostic LEDs, When I connect the power cord to the iMac, the first LED illuminates. Then, when I press the power button, the second LED lights up. However, the third and fourth LEDs in the sequence do not turn on.

I've actually tried taking out the RAM and giving it a shot, and guess what? It actually beeped, just like it's supposed to! So, I don't think it's completely dead after all.

Next up, I'm gonna swap out the PRAM battery, even though I'm not entirely convinced that's the problem. I might also replace the RAM, but here's the thing—I don't have the right RAM on hand. Do you know of any other way to test those RAM sticks? I'll take off the Airport card and give it a shot. I'm curious to see if removing it will have any impact. Any tips would be awesome!

By the way, a little backstory on this iMac. It actually belonged to a friend of mine, but it's been gathering dust on his desk for ages. Apparently, he stopped using it around 4 or 5 years ago and stashed it away in a garage or something like that. Unfortunately, it was exposed to high humidity due to its proximity to the sea, which only made oxidation worse. Becouse of that, I'm thinking of going for the rather boring option of completely disassembling everything and cleaning each piece with alcohol. It might seem a bit radical, but I'm considering it as a last resort.

So, after being neglected for all those years, he decided to give it another shot, and you know what? It actually started up and ran for a little while before unexpectedly shutting down. Years later, here I am, stepping in like a tech wizard, attempting to work my magic and bring this forgotten iMac back to life. Who knows? Maybe I can pull off a miraculous revival here!