When your internal hard drive refuses to mountboot or data in it decline to open up then it could be due to any of above mentioned or some unknown reason If you backup internal hard drive data regularly then it is appreciateable

Please fix the punctuation.
When your internal hard drive refuses to mount/boot or data in it decline to open up, then it could be due to any of above mentioned or some unknown reason. If you backup internal hard drive data regularly, then it is appreciateable.