I have a raspberry pi 3 that I have used successfully for several years now. A few months ago, I left it in the attic (often very hot here in Florida). I took it out recently and tried to start it up again, and it won't boot. I see the red light come on; the green activity light flashes twice, then flickers weakly and dies. The TV (hdmi connection) shows a rainbow screen. I've read the entire 'STICKY' article (long and short versions), and all I have been able to glean from it is that for some reason the pi is trying to boot from the card, and failing. I haven't re-imaged the SD card, but I have made sure that it wasn't corrupted using a Macbook with disk utility.
I haven't changed the configuration of the pi, except for the fact that I'm using a new TV. The SD card and everything else was unaltered from the way I was using it pre-attic. I'm worried that the attic may have killed it, though I've read other posts from people operating a pi in an attic saying that it should withstand operating temperatures up to 85C (185F), and I doubt that my attic was ever that hot. It was in a case (always has been), and didn't even have much dust.
Things I have tried:
Verifying that the SD card wasn't corrupted using a Macbook with disk utility
Checking that the power supply (came with the pi) was good
Checking the 3V3 port for adequate voltage
Making sure 'start.elf' was present on the SD card
and a few others that I can't remember
Any ideas? Could the attic have killed it? Could it have killed the SD card--even though I checked for corruption? Am I missing something (possibly even from the STICKY article)?