This question already has an answer here:
I recently installed Raspbian on my Raspi B+ and everything - including external usb hub with 2 usb hdds - worked fine. Today, I realized that I could not access the Raspi via LAN (cable) and that the red and green led shined continuously. I made a research and tried all advices, but noting worked. I removed the micro SD and windows explorer shows that it has a size of 56 mb (instead of 16 gb) and there are hardly no files on it:
(folder overlays is empty)
Is this normal? If yes, why else wouldn't it boot? If no, what can I do apart from re-installing the os?