Its most probably due to file system corruption and device is not able to read the config files. The best solution would be to recover the device using a snapshot taken from another device.
Step 1. Plug in a USB drive (2-8 GB) to the working device Step 2. Take snapshot to usb using following command "srx> request system snapshot media usb partition Step 3. Once snapshot is complete, plug in this USB to faulty device and power cycle the same. The device will try to boot up from USB Step 4. Once the device boots up copy the snapshot from USB to internal flash using "srx> request system snapshot media internal partition" Step 5. Once the above step is completed, unplug the USB and try power cycle the device to make sure it boots up successfully
Thanks, Suraj Please Mark My Solution Accepted if it Helped, Kudos are Appreciated too