Maybe the problem is related to the micro SD card (for example, corrupt data due to an uncontrolled shutdown).
I recommend to repair the two partitions ( vfat boot and ext4 root) of the SD card. You will need a Linux system (PC, Live DVD, virtual machine, RPi, etc) for such procedure.
If you have more SD cards, try installing a new raspbian on your RPi. If this new install works, your RPi is not damaged.