One of my Pi cards stopped booting, obviously not a hardware fault, I do different projects on a selection of cards as it makes life and management a lot easier.
Ah yes rtl-sdr software defined radio. Repurpose a USB TV tuner as the front end for an SDR, use the Pi to connect it to the network and use another machine (reasonably specced laptop) to do the decoding.
This was the card I'd been using the Pi as an SDR server, so I'd downloaded Gnuradio for some of the modules I was playing around with. I have one of those TV dongles so off I went and had a go. Trouble is, it sorted of bloated itself. One partition on the card was full. Hence no boot.
I removed the offending folder manually, ran fsck, and it's back to life.