Never fear, a solution is here! *gets pipiaked*
Problem: My Sansa Clip+ (aka Sansa Clip Plus), Mort, died while I was listening to the Devil Survivor Drama CD. In the middle of playing a chapter, it suddenly died and refused to turn on. Plugging it into the computer showed no responses via USB and the computer didn’t recognise the Sansa Clip+ plugged in.
Here’s a common solution that worked for me:
1. Press and hold the Power button for 20 seconds or more.
2. Release the button, count to 2.
3. Switch your Sansa Clip+ back on.
Marauderz suggested that Mort’s battery could have hung which was the reason why the hard reset worked. I suspect that’s the case, as Mort died when trying to play a corrupted file (which has since been removed).