I'll skip over #2. The B+ is connected to a large breadboard with an Arduino Nano stuck on it with USB between the Pi and the Nano -- the Nano doing analog devices. The whole setup is for trying new things.
Back to #2: this one sits in a 6" x 8" x 3" lexan box. I use it as a portable example of what you can do with a Pi (see my post 55). It is connected to a variety of devices: LEDs, PIR motion detector, temp sensor, Pi camera, clock-type 7-segment display, a 2-relay switch, a speaker for voice synthesis output, plus battery power.
And it's #2 that has failed. It had been collecting dust (not inside it's box), unplugged for 2-3 months. But I wanted to use the camera so I plugged it in and only the little red power light came on. I took the SD card out and checked it on Pi #1 with fsck. It seemed ok. So, I moved a backup SD to #2. No good. Doesn't ever find the SD card. I tried other useless stuff. Nothing. I vaguely remembered something about the Pi's SD pins getting flattened to where contact fails. Must be what happened.
So I took the nice setup apart. Nasty. The Pi was screwed down to a board. Then I messed with the SD pins on the under side of the Pi -- tried to pry them up a bit. The original SD endlessly tries to boot -- and fails. The backup SD from my Pi#1 works but the setup is all wrong. Crap.
Got a new 16gb SD card. copied Pi#1 data to it (see post 48). Changed all the files (/etc/hostname, /etc/network/interfaces, etc.). Copied Pi#2 data from backup. Inserted new card. It worked. Gimme back the hours wasted.
2 other things:
* The new SD: plastic shell seems a tiny bit thicker.
* I'd forgotten: at some point I had added a layer of tape on the non-contact side of Pi#1's SD card. It must have given me trouble. No wonder later Raspberry Pis went to the micro SD plug.