Two Pis, multiple displays, multiple HDMI cables, no boot/display

[PineyCreek]

I've got both a Raspberry Pi 2B and a 3B+.  They've sat for a while without being powered on (climate-controlled, low humidity).  When I last used them, both worked fine.

 

When I tried turning them on recently, they either don't finish boot or don't put out a display.  With the 3B+ at least, I can hear the attached fan powering on and varying speed a bit.  The red LED lights up, but no activity light, and nothing on the ethernet port.  I have tried both with multiple power supplies (both at 5V 2.5A max output) at multiple outlets, tried with multiple HDMI cables and multiple displays both TV and computer monitor.  To coincide with the lack of activity on the ethernet port, I also do not see a new device on the network nor one of the Pis' configured device names.

 

I'm not sure how both of these can go bad suddenly, so I must be doing something wrong, or I have tremendously bad luck.  Any ideas?  The one thing I have not yet tried is checking the microSD cards in either of them, which have remained in their respective Pis' card slots.  They are fully-inserted.

 

UPDATE: Well, nevermind.  I solved my problem.  Took the microSD card out to check the boot partition, found it was fine.  Forced HDMI though it wasn't necessary before and I wanted to say I had done something.  Put the card back in and no issues with starting it up...I imagine it was just reseating the card considering before it wasn't even starting the network stack and no activity lights.  These weren't stored in a high-humidity or hot environment so I'm not sure why reseating it worked.

Then again I suppose I'm not sure sometimes why power cycling somethings works as often as it does, even though I've been in tech support in some fashion for decades >_>